ALBERT

Description: The results of this study show that close boats (〈100 m) affect the behaviour of bottlenose dolphins more strongly than boats further away (〉100 m). Close boats induced a decrease of feeding, resting and social behaviour. The proportions of high-speed swimming and slow swimming increased. In the presence of close boats, dolphins were observed 6 times more frequently to leap and 3.6 times more frequently to tail-slap than under control conditions – an indication of disturbance. Dolphins responded to close boats with evasive manoeuvres similar to techniques used for avoiding predators. With more than two close boats, animals swam approx. 37% faster than without close boats. An energy consumption of 2.93 W kg-1 was calculated. This corresponds to a daily energy demand of 50.6 MJ per dolphin with 200 kg body weight. With boats at close range, the mean power requirement of dolphins was around 15.4% higher than during controls. With close boats, dolphins used a third of their energy budget to avoid boats by swimming at high speed. In the light of these findings, recommendations for dolphin-watching guidelines are given.

Description: Die vorliegende Arbeit untersucht die Veränderung der Sturmtätigkeit über den Weltmeeren im Zeitraum von 1889 bis 1997. Hierfür wurden Luftdruckbeobachtungen aus Schiffsmessungen des Comprehensive Ocean-Atmosphere Data Set (COADS) verwendet. Untersuchungen deuten darauf hin, dass die Bestimmung von langfristigen Trends in Beobachtungsdaten durch die geringe Anzahl von Beobachtungen vor 1950 erschwert wird. Ein Schwerpunkt dieser Arbeit lag deshalb darauf, mit Hilfe von Monte-Carlo-Rechnungen die Fehler abzuschätzen, mit denen aufgrund der Schwankungen in den Beobachtungszahlen zu rechnen ist. Aufgrund der gewonnenen Erkenntnisse unter Einbeziehung der abgeschätzten Fehler kann nur davon ausgegangen werden, dass es im nördlichen Bereich des Nordatlantiks zu einer Intensivierung der Sturmtätigkeit in der Zeit von 1889 bis 1997 gekommen ist. Die Größe der abgeschätzten Fehler deutet darauf hin, dass es unbedingt erforderlich ist, diese Fehler zu berücksichtigen, um sichere Aussagen über langfristige Trends von Beobachtungsdaten mit stark veränderlicher Datendichte treffen zu können.

Description: Ziel dieser Arbeit war es, die Prozesse der Sedimentveränderung an konvergenten Plattenrändern zu charakterisieren. Dafür wurde ein Profil vor der Küste des südlichen Costa Ricas gewählt. Entlang dieses Profils wurden seismische Reflexionen sowohl für den Steilwinkel- als auch für den Weitwinkelbereich aufgezeichnet. Durch Modellierung der Reflexionsamplituden konnten die seismischen Geschwindigkeiten entlang dieser Plattengrenze ermittelt werden. Es zeigt sich, daß die Kompressionswellengeschwindigkeit unterhalb des Decollements um ca. 15% entlang des Profils variiert, während die Scherwellengeschwindigkeit im gleichen Bereich eine Variation von 50% zeigt. Variationen dieser Größenordnung können nur durch Unterschiede in den Porendrücken des Sediments erklärt werden. Ein Vergleich mit Labormessungen zeigt, daß der effektive Druck im subduzierten Sediment Werte zwischen 1 und 7 MPa erreicht. Der Grund für diese räumlich sehr kleinen Druckunterschiede ist eine lokal stattfindende Tonmineralumwandlung.

Description: Large volumes of mainly felsic volcanic ashes have been repeatedly released during explosive volcanic eruptions along the Central American Volcanic Arc. These ashes are found as up to several centimetres thick ash layers in marine sediments offshore Nicaragua and Costa Rica. Since volcanic ashes constitute such a major fraction of slope sediments and subducted deep sea sediments off Nicaragua and Costa Rica its alteration is significantly affecting the chemical signatures of sediments and pore waters. New results of mafic and felsic glass alteration were derived from extensive field investigations of marine tephra. deposits and diagenetic processes in related pore waters as well as laboratory dissolution experiments.

Description: Within the framework of this thesis the investigation of methanogenesis and secondary degradation processes of methane in two distinctly different marine environments has been carried out. These two environments were (i) the gassy shallow-marine sediments of the Arkona Basin, western Baltic Sea and (ii) the hydrothermal submarine fluid/gas exhalations at hotspot volcanoes of the central South Pacific. Based on the results of geochemical, sedimentological and seismic investigations as well as geochemical modelling it was possible to reconstruct the occurrence, distribution, genesis and degradation processes of methane in these two environments. Particularly, the analyses of the molecular composition of the hydrocarbons extracted from the fluid/pore water in combination with the stable carbon and hydrogen isotopic signal enabled deductions regarding the methane formation processes in the respective working areas. In the central Arkona Basin an area of about 1500 km2 shows acoustic turbidity of the seismic signal in ~1.5 m depth in the surface sediments. This acoustic turbidity is an indication of free gas in post-glacial surface sediments which may reach about 12 m thickness in the basin centre. These sediments are characterised by a conspicuously high organic carbon content (ca. 5-8 %) and a clayey-silty structure. The degradation of organic matter produces anaerobic conditions in near surface sediments and in about 1 m sediment depth, below the sulphate reduction zone, it results in the accumulation of methane. The stable carbon and hydrogen isotopic results of all gas samples from the post-glacial sediment layer confirm bacterial methane production via CO2 reduction. Solely, the d13C-CH4 values of ~-40‰ of the upper few centimetres of the surface sediments indicate oxidised methane. The late- and post-glacial clay (reddish/brown and grey) that is located beneath the organic-rich sediments, however, shows rather low methane concentrations within the pore-water and the concentration profile as well as the d13C-CH4 values point to diffusion of gas from the surface sediments in to the clay. Overall, the measured methane concentrations in pore-water show distinct differences in methane concentration from trace concentrations at the northern rim of the basin to the point of methane saturation in the central basin. The increase in CH4 concentration is generally accompanied by an increasing thickness of organic-rich surface sediments. Based on the concentrations of organic carbon, methane, and sulphate and the average sedimentation rate a numerical model was developed to characterise sulphate reduction, anaerobic oxidationof methane and methane production. The model results show that a sediment thickness of 3.5 m has to be achieved to obtain CH4 production rates that enable the accumulation of methane in the sediments. Furthermore, it could be shown that a sufficient amount of methane required to cause oversaturation and gas bubble formation can not be generated until a sediment thickness of 5-6 m is reached. This minimum sediment thickness established by the geochemical model correlates nicely with the sediment thickness at which the seismic readings show acoustic turbidity. During research cruises Sonne 65 (1989) and Polynaut (1999) methane analyses were conducted on water column and fluid samples above submarine volcanoes of the Pitcairn, Austral, and Society island chains, central South Pacific. Weak hydrothermal activity was determined at hotspot volcanoes Bounty and Teahitia in 1999. The 1999 results, in comparison with methane results from 1998, point to a rather calm exhalation activity of the hotspot volcanoes. The higher methane concentrations determined in the water column in 1998 could be attributed to the eruption of the Macdonald seamount that occurred at that time. The importance of bacterial methane production by CO2 reduction, also for hot exhalations of submarine volcanoes, could be described the first time by means of the 13C/12C and D/H isotope ratios of methane. At the Bounty seamount the stable isotopic values of methane from the fluids refer to an almost 100% bacterial production of methane at about 88°C. An amount of about 50% bacterially produced methane besides the abiogenic produced methane could be determined at Macdonald seamount.

Description: In dieser Arbeit wird der Einfluß durchbrochener Bewölkung auf die solaren Einstrahlung am Boden untersucht. Die zugrundeliegende Messkampanie wurden im Rahmen einer interdisziplinären Zusammenarbeit des Leibniz-Instituts für Meereswissenschaften (IFM-GEOMAR) mit dem Institut für Medizinische Klimatologie der Universität Kiel im Sommer 2004 (18. Juni - 16. September) auf der Nordseeinsel Sylt durchgeführt. Dabei wurde die Wolkenkamera des IFM-GEOMAR zur Erfassung der Wolken im kompletten Halbraum über der Kamera verwendet. Die notwendigen Bedeckungsgraddaten wurden mithilfe eines FORTRAN77 Programms aus den Bildern der Wolkenkamera, die alle 15 Sekunden vorliegen, bestimmt. Aufgrund von Streulichteinflüßen durch die verwendete Acrylkuppel und der relativ geringen Auflösung der Helligkeitswerte sind die Kameradaten fehlerbehaftet und bedurften einer genauen Nachbetrachtung. Dank der hochaufgelösten 2-sekündlichen Strahlungsmessungen konnten Strahlungserhöhungen von bis zu 481 W/m2 gegenüber der theoretischen Referenzstrahlung bei wolkenfreiem Himmel festgestellt werden. Die maximalen Werte traten bei recht unterschiedlichen Bedeckungssituationen auf, wobei eine Korrelation von 0,4 zwischen Strahlungserhöhungen und Bedeckungsgrad bestimmt wurde. Im Mittel wurden die stärksten Strahlungserhöhungen bei etwa 84 % Bedeckung erreicht, was mit den Ergebnissen von Estupinan et al. (1996) übereinstimmt. Die Bestimmung der Wolkenstruktur aus den Kameradaten wurde mithilfe einer Fläche/Umfang-Beschreibung der Wolken, dem Homogenitätsgrad 'HG', und der fraktalen Box-Dimension 'D' versucht. Die Ergebnisse scheinen den von Sabburg und Wong (2000) gefundenen Zusammenhang zwischen Strahlungserhöhung und Wolkentyp zu stützen. Hiernach treten die maximalen Werte bevorzugt bei cumulusartiger Bewölkung in den unteren und Cirren in den hohen Schichten auf. Die Cirruswolken führen dabei zu einer erhöhten diffusen Strahlung und somit auch zu einer erhöhten Reflexion and den Wolkenseiten der tieferen Cumuluswolken. Die Korrelation zwischen Strahlungserhöhungen ≥ 300 W/m2 und HG sind allerdings mit Werten von 0.2 nicht aussagekräftig. Die Berechnungen der fraktalen Box-Dimension scheinen zudem noch fehlerbehaftet und bedürfen näheren Untersuchungen. Weiterführende Untersuchungen am IFM-GEOMAR mit einer verbesserten Kamera sollten künftig deutlichere Ergebnisse liefern.

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: 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.