ALBERT

Description: For simple analysis of stochastic climate models the ocean is often forced with a statistical atmosphere model. The atmosphere model mimics the observed statistics of the atmospheric forcing, e.g. the heat fluxes and the wind stress. This study serves as the beginning of the development of such a global statistical atmosphere model. The starting point of the development is a Monte-Carlo-like model written by Dietmar Dommenget, which is coupled to an one-dimensional model of the upper ocean. An important question in this context is how good the existing model simulates the atmospheric forcing. For that purpose the probability distribution functions of the net heat flux and the wind stress (respectively the surface fricion velocity u* ) derived from observations and a coupled run of the GCM ECHAM5 with the above mentioned ocean model are examined. The results are compared to the output of the statistical atmosphere model. The spatial and temporal patterns of the statistical moments mean, standard deviation, skewness and kurtosis are considered particularly. The investigation of the moments shows considerable differences between the model data and the observations. Especially the wind speed and thereby the friction velocity of the observations differs from that calculated by ECHAM5. The distributions of the friction velocity simulated by the statistical model deviate from both the observations and the ECHAM5 model data. By performing sensitivity studies it is shown that the deviations between the probability distribution functions have a non-negligible influence on the evolution of the sea surface temperature. The results of this analysis lead to possible modifcations of the statistical atmosphere model. Two different atmosphere models including these modifcations are presented. Another approach for the development of a statistical model, the usage of spatial correlation patterns is elucidated. Because of the enormous number of EOF modes needed to reach 90 percent of explained variance, even in the coupled EOF analysis between u* and the netflux, it is refrained from developing a statistical atmosphere based on these EOF modes. Finally an atmosphere model based on the bulk formulas is formulated as a result of a cross spectral analysis, which indicates an underrepresentation of the low-frequency variability in the SST time series caused by the direct forcing of the ocean with the surface fluxes. The SST time series simulated by this model exhibit a much higher coherency with the SST of the ECHAM5 model run.

Description: To assess the impacts of climate change on phytoplankton autumn successions, an experimental analysis using Baltic Sea plankton was undertaken in eight 1400 l indoor mesocosms situated in four climate chambers, running for 40 days in November/December 2005. The temperature baseline was defined according to the average local conditions in the past eight years. In two mesocosms, the temperature was regulated according to this baseline. For two mesocosms respectively, a warming of 2, 4, and 6°C was simulated in three different climate chambers. A light regime simulating natural daylength, dim phases at dawn and dusk, and randomized cloud cover was established. Phytoplankton was sampled three times per week, fixed by Lugol's iodine, counted and identified, and chlorophyll a values were measured. In parallel, a sample from the Kiel Fjord was taken on each sampling day and treated accordingly. Abundance, mean specific cell volume, total biovolume and biomass were calculated for each taxon in the respective treatments. Taxonomie richness and biodiversity measured as Shannon Wiener Index were determined. Biomass and chlorophyll a peaks and timing of these peaks were correlated with temperature, as were decrease in species richness and lass in biodiversity. Microphytoplankton was the dominating size class, diatoms (up to 500 cells/ml) were clearly predominant over dinoflagellates (never more than 5 cells/ml). Within the Bacillariophyceans, the genus Coscinodiscus contributed more than 75 % biovolume in the start of the experiment, and its proportion increased throughout the experiment in all mesocosms. In warmer treatments, biomass as well as chlorophyll a peaks tended to occur earlier and were lower than in colder treatments. A post bloom biomass minimum only developed in the four warmer treatments within time of experimentation, indicating that this phase was even more strongly accelerated by temperature than were the peak conditions. Numbers of taxa and biodiversity steadily decreased in all treatments, yet more steeply so in warmer treatments. Hence it was derived that species lass was also slightly accelerated by temperature. Through match-mismatch events these temperature dependent alterations in phytoplankton abundance and composition may affect higher trophic levels and thus have an impact on the whole food-web. Temperature enhanced lass in biodiversity may have impacts on invasion resilience of a phytoplankton succession or on its capacity to sustain a divers grazer community.

Description: The goal of the here presented study was to elucidate the effect of temperature on the production and lass mechanisms of dissolved organic matter in a microalgal culture. For this purpose, an axenic diatom culture was grown in North Sea water containing a natural bacterial community and exposed to three different temperatures (17°C, 21°C and 26°C). During the following 25 days the development of algal growth and bacterial activities as weil as changes in the concentration of DOC, carbohydrates and TEP were closely followed. The here obtained results show a clear dependence of the autotrophic and heterotrophic processes on temperature. At the highest temperature, algae grew about two times faster than those incubated at the lowest temperature. The overall produced amount of algal biomass did not differ between the three temperature incubations as indicated by the concentration of POC. Contrary to this, algae growing at the lowest temperature produced considerably less Chi a than those at the highest temperature. lt is suggested that cells growing at their lower temperature limit cannot efficiently use large amounts of light energy captured by photosynthesis, because their intracellular processes are considerably slowed down. Thus, by producing less Chi a they absorbed less light energy at a time, but used it efficiently to build up biomass over a langer period of time. All cultures reached a situation of nutrient depletion in the course of the experiment. The ratio of C: N rase up to values of ~20:1. Thus, the extracellular release of carbon-rich dissolved organic compounds was highly probable. Astonishingly, no effect of temperature on the pools of DOC and carbohydrates could be observed. Interestingly, the production of TEP was influenced by temperature. An increase by 9°C led to a more than two-fold increase in the amount of TEP produced. Based on this finding it is suggested that the production of TEP exhibits a temperature-sensitivity that is on the same scale as heterotrophic processes. Thus, the hypothesis that the production of TEP could be reduced at elevated temperatures due to a faster uptake of DOM by bacterial processes, has to be rejected. A decrease in POC and TEP at the highest temperature was observed in the second half of the experiment, whereas bacterial activities increased. High activities of bacterial a-Dglucosidase and ß-D-glucosidase suggest that a considerable amount of carbon-rich DOM was exuded in the course of the experiment. In summary, the data of DOC cannot be explained to this point of time. An increase in temperature clearly affected the dynamics in the autotrophic and the heterotrophic processes. Since even the pool of TEP was positively influenced, it seems likely that temperature has an effect on the pool of DOM.

Description: Der Einfluss der Temperatur auf die Mortalitäten zeigt sich im zeitlichen Verlauf. Bei höheren Temperaturen erreichen die Mortalitäten schneller ein Maximum als bei niedrigen Temperaturen. Die Dottersacklarven des Hungerexperimentes zeigten bei Temperaturen von 11,7°C bis 15,5°C den schnellsten Verbrauch der Dotterreserven, bei 3,5°C und 5,7°C war bei 12 Tage alten Larven noch Dotter vorhanden. Anhand der Mortalitäten und der RNA/DNA-Verhältnisse konnte bei 13,6°C und 15,5°C nach acht Tagen ein deutliches Hungern bestätigt werden, bei 9,7°C und 11,7°C nach elf Tagen. Dies zeigte sich auch anhand des immer stärker abnehmenden Trockengewichtes. Bei 7,7°C konnte nach 11 Tagen der Beginn eines Hungereffektes beobachtet werden, bei 3,5°C und 5,7°C war nach 11 Tagen noch kein Hungereffekt sichtbar. Bei 10,5°C und 13,6°C zeigten jüngere Heringslarven sowohl das beste Längenwachstum als auch das höchste Trockengewichtswachstum. Bis zu einem Alter der jüngeren Heringslarven von 10 Tagen, ähnelte das RNA/DNA-Verhältnis dem von hungernden Bei Temperaturen von 11,5°C und 12,6°C konnte für jüngere Heringslarven die beste Kondition in der Kleinen Temperaturorgel ermittelt werden. Die Hungerparallele zeigte das schlechteste RNA/DNA-Verhältnis und die geringste Trockengewichtswachstumsraten. Die jüngeren Heringslarven in der grünen Tonne zeigten die höchsten RNA/DNA-Verhältnisse und das höchste Wachstum. Das Längenwachstum der älteren Heringslarven des Futterexperimentes zeigte große Streuungen. Bei Temperaturen zwischen 10,5°C und 13,6°C konnte das höchste Trockengewichtswachstum ermittelt werden. Eine Temperatur von 16,3°C erwies sich als kritische Temperatur für heranwachsende Heringslarven. Das beste RNA/DNA-Verhältnis und das höchste Trockengewicht zeigten ältere Heringslarven, die bei 11,5°C gehältert wurden. Die Hungerparallele zeigte auch bei den älteren Heringslarven die geringsten RNA/DNA-Verhältnisse. Es wurden bei beiden Futterexperimenten sowohl hungernde, schlecht fressende und gut fressende Heringslarven beprobt. Es konnte bei den Selektionsexperimenten bei den jüngeren und älteren Heringslarven keine Abhängigkeit der Nahrungsaufnahme vom Alter festgestellt werden. Sowohl die jüngeren als auch die älteren Heringslarven zeigten keine Bevorzugung eines bestimmten Nahrungsorganismus. In den untersuchten Därmen der Heringslarven stellten Nauplien, Rotatorien und Bivalvia-Larven die wichtigsten Organismen dar. Das Wachstumsmodell zeigte eine lineare Abhängigkeit zwischen dem RNA/DNA-Verhältnis, dem Wachstum und der Temperatur.

Description: Fontana Tephra has been generated by a large basaltic-andesitic plinian eruption in the Late-Pleistocene in the Masaya area, west-central Nicaragua, at the Central American subduction zone. The eruption evolved through several plinian fallout phases, alternating with phreatomagmatically-affected plinian fallout activity. The minimum estimate of the total erupted tephra volume amounts to 1.4 to 1.8 km3. Comparisons of tephra dispersal parameters with theoretical modelling results suggest eruption column heights between 24 and 30 km. The eruption was powered by exsolution of magmatic water. The gas chemistry of melt inclusions and matrix glasses as determined by SIMS, supported by petrographic observations, indicate a retarded degassing process in disequilibrium with the pressure release during magma ascent in the conduit, associated with a substantial volatile supersaturation. This sudden vesiculation process, combined with the high temperature and rapid ascent of the magma is considered to be responsible for the unusual plinian eruptive style of the mafic Fontana magma. High magmatic bromine and iodine contents, positively correlating with high Ba-La ratios, indicate strong sediment recycling through the subduction zone.