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Trace elements incorporation of certain trace elements like strontium (Sr) and magnesium (Mg) among others and their isotope composition in different CaCO3 polymorphs (e.g. calcite and aragonite) as archives provide valuable for proxy information, that can be used as important tools for reconstructing the paleo- environmental conditions of the oceans throughout time. However, data on Sr incorporation into inorganic precipitated CaCO3 (calcite and aragonite), Mg incorporation into aragonite and Sr isotopic fractionation during minerals formation are still very rare. In addition, literature values available concerning Ca isotopic fractionation between calcite and aqueous solution are discrepant to a certain extent, while on the other hand the data available concerning Ca isotopic fractionation between inorganic precipitated aragonite and aqueous solution are also scarce. In order to overcome this lag of information in this study calcite and aragonite were precipitated at three different temperatures (12.5, 25.0 and 37.5±0.2 °C), different precipitation rates (R*) and solution composition by diffusing NH3 and CO2 gases into aqueous solutions containing trace elements and NH3 ions. For the kinetic study we used the initial rate method to solve the rate equations (rate law) with R* values in the range between 2.5 to 4.5 μmol/m2.h. We find that both calcite and aragonite have exactly the same order of reaction only differing in their activation energy (114 kJ/mol for calcite and 149 kJ/mol for aragonite) and rate constants at 25 °C (80.6*10-4 for calcite and 17.3*10-4 mM-2.h-1 for aragonite). The order of reaction with respect to Ca2+ ions is ≈ 1 and temperature dependent, while the order of reaction with respect to HCO3- ions is temperature dependent decreasing from 3 via 2 to 1 as temperature increases from 12.5 via 25.0 to 37.5°C, respectively. Calcium isotope fractionation for both calcite and aragonite (Δ44/40Ca) was found to be R* and temperature dependent. For 12.5 and 25.0 °C we observe a general increase of the Δ44/40Ca values as a function of R*, whereas at 37.5 °C decreasing Δ44/40Ca values are observed relative to increasing R*. It is suggested that the temperature triggered change from a Ca2+-NH3-aquacomplex covalent controlled bonding to a Ca2+-H2O-aquacomplex van-der-Waals controlled bonding caused the change in sign of the R* - Δ44/40Ca slope due to the switch of an equilibrium type of isotope fractionation related to the covalent bonding during lower temperatures to a kinetic type of isotope fractionation at higher temperatures. This behavior of Ca is in sharp contrast to the Sr isotopes which do not show any change of its fractionation behaviour as a function of complexation in the liquid phase. For both polymorphs of CaCO3 as a function of increasing R* the Δ88/86Sr-values become more negative and as temperature increases the Δ88/86Sr values also increase at constant rate. However effect oft R* on the Δ88/86Sr values is more significant in calcite than in aragonite. Magnesium incorporated into aragonite (expressed as DMg= [Mg/Ca] aragonite/ [Mg/Ca] solution) increases with decreasing temperature and also increases with increasing R* and as temperature increases the R* effect decreases. Later behavior is opposite to Mg in calcite (as temperature increases DMg also increases) as already known from earlier studies. Strontium incorporated into both calcite and aragonite (expressed as DSr= [Sr/Ca] solid/ [Sr/Ca] solution) was found to be R* and temperature dependent. Rate effect is more dominant over temperature effect in calcite, while on the other hand temperature effect is more dominant over rate effect in the case of aragonite. In calcite DSr increases with increasing R* and decreasing temperature. In aragonite also DSr increases with decreasing temperature. However concerning R* it responds differently: at 37.5°C DSr as R* increases DSr values increase, but decrease at 12.5°C. At 25.0°C, both behaviors are detected depending on the molar [Sr]/[Ca] ratio of the reacting solution (0.005 or 0.01). In the frame of a qualitative model to explain our trace element and isotope observations we speculate that increasing Mg2+ -concentrations control the material flux back (R*detach) from the crystal to the solution to a large extend. As a consequence R* values for aragonite tend to be lower than for calcite as observed from our data. Hence, Sr incorporation into aragonite is affected as function of temperature to a higher degree when compared to the R* effect. This is also reflect on the Δ88/86Sr values and decreasing the R* effect when compared to the temperature effect. Moreover concerning Ca isotope fractionation, the switch of direction in Ca isotope fractionation above ~25°C may be either due to the Mg2+ blocking effect or due to the switch of complexation from NH3 at and below 25 °C to H2O complexation at 37.5 °C. Plotting DSr versus Δ88/86Sr may be used as a proxy to reconstruct precipitation rates of calcite and of precipitation temperature of inorganic aragonite. Latter correlation may also have important implications for the verification of CaCO3 diagenesis.

Radiogenic lead (Pb) and neodymium (Nd) isotopes are sensitive paleoceanographic proxies for the reconstruction of ocean circulation changes in the past. The goal of this dissertation is to develop improved approaches to recover past seawater Pb and Nd isotope signals from marine sediments and ferromanganese (Fe-Mn) crust, and apply it for tracing water mass sourcing changes in the Southern Ocean at (sub-)millennial resolution.

keine engl.-spr. Zusammenfassung vh. Die vorliegende Arbeit untersucht den Einfluss der Wolken auf die Fernerkundung des Wasserdampfes. Globale Klimatologien des Wasserdampfes sind auf Messungen im infraroten Spektralbereich aufgebaut. Hier sind Wolken undurchlässig, daher müssen bewölkte Szenen bei der Ableitung der Klimatologie ausgeschlossen werden. Dadurch kommt es zu einer Unterschätzung des Wasserdampfes, da bewölkte Szenen mehr Wasserdampf enthalten als unbewölkte. Diese Unterschätzung wird in dieser Arbeit quantifiziert. Aus Messungen des Mikrowellenradiometers AMSU werden sowohl im bewölkten als auch im unbewölkten Fall der Wasserdampf über den Ozeanen bestimmt.

This thesis focuses on the eco-evolutionary processes that drive novelty, using the Caribbean hamlets as a model system to answer this question.

Unveiling the factors and processes that shape the dynamics of host associated microbial communities (microbiota) under natural conditions is an important part of understanding and predicting an organism's response to a changing environment. The microbiota is shaped by host (i.e., genetic) factors as well as by the biotic and abiotic environment. Studying natural variation of microbial community composition in multiple host genetic backgrounds across spatial as well as temporal scales represents a means to untangle this complex interplay. Here, we combined a spatially-stratified with a longitudinal sampling scheme within differentiated host genetic backgrounds by reciprocally transplanting Pacific oysters between two sites in the Wadden Sea (Sylt and Texel). To further differentiate contingent site from host genetic effects, we repeatedly sampled the same individuals over a summer season to examine structure, diversity and dynamics of individual hemolymph microbiota following experimental removal of resident microbiota by antibiotic treatment. While a large proportion of microbiome variation could be attributed to immediate environmental conditions, we observed persistent effects of antibiotic treatment and translocation suggesting that hemolymph microbial community dynamics is subject to within-microbiome interactions and host population specific factors. In addition, the analysis of spatial variation revealed that the within-site microenvironmental heterogeneity resulted in high small-scale variability, as opposed to large-scale (between-site) stability. Similarly, considerable within-individual temporal variability was in contrast with the overall temporal stability at the site level. Overall, our longitudinal, spatially-stratified sampling design revealed that variation in hemolymph microbiota is strongly influenced by site and immediate environmental conditions, whereas internal microbiome dynamics and oyster-related factors add to their long-term stability. The combination of small and large scale resolution of spatial and temporal observations therefore represents a crucial but underused tool to study host-associated microbiome dynamics. © 2016 Lokmer, Goedknegt, Thieltges, Fiorentino, Kuenzel, Baines and Wegner.

The aim of this thesis is to explore and understand some major climate mechanisms that were responsible for atmospheric and oceanic changes during the LGM (21,000 years ago). A coupled global atmosphere ocean model of intermediate complexity is used to study the influence of glacial boundary conditions on the climate system during the LGM in a systematical manner. A web of atmospheric interactions is disentangled which involves changes of the meridional temperature gradient and an associated modulation of the atmospheric baroclinicity. This in turn drives anomalous transient eddy momentum flux which feedback onto the zonal mean circulation. Moreover, the modified transient activity, weakened (strengthened) in the North Pacific (Atlantic), leads to a meridional re-organization of the atmospheric heat-transport, thereby feeding back to the meridional temperature structure. Furthermore, it is argued that modifications of the large-scale atmospheric circulation during the LGM may have led to a slowdown of the Pacific subtropical gyre as well as to an intensification of the Pacific subtropical cell. These oceanic circulation changes generate an eastern North Pacific warming, an associated cooling in the Kuroshio area, as well as a cooling of the tropical oceans, respectively. The tropical cooling pattern resembles a permanent La Nina state which in turn forces atmospheric teleconnection patterns that lead to an enhancement of the subtropical warming by reduced latent and sensible cooling of the ocean. In addition, the radiative cooling due to atmospheric CO2 and water vapour reductions imposes a cooling tendency in the tropics and subtropics, thereby intensifying the permanent La Nina conditions. Hence, a delicate balance between oceanic circulation changes, remotely induced atmospheric flux anomalies as well as local radiative cooling is established which controls the tropical and the North Pacific temperature anomalies during the LGM. The LGM simulation exhibits an intensified Atlantic overturning cell, associated with an enhanced formation of North Atlantic Deep Water. This enhancement can be attributed to the strong surface cooling in high latitudes and brine release in areas of seasonally varying sea-ice extent. In turn, the intensified meridional overturning circulation leads to an enhanced poleward heat transport that is required to equilibrate the strong tropical-extratropical temperature contrast during the LGM. The modeling results compare well with some recent paleoreconstructions.

Gas hydrates are fascinating ice-like compounds made of water cages that retain various types of guest molecules. Natural gas hydrates on Earth form below the seafloor and permafrost and contain mainly methane (CH4). Methane from hydrate deposits could be considered as an energy resource. One possible production scenario of CH4 from hydrates is the injection of carbon dioxide (CO2) or carbon dioxide-nitrogen(CO2-N2) mixed gas into the reservoir. Depending on the thermodynamic constraints, the composition of the gas hydrate guest molecules changes: the energy source CH4 is released and the greenhouse gas CO2 is trapped. The aim of the present work is to study the mixed gas hydrates that form in gas hydrate reservoirs after injection of CO2 or CO2-N2 gas mixtures, using laboratory experiments and modeling.

Increasing atmospheric CO2 concentrations equilibrate with the surface water of the oceans and thereby increase seawater pCO2 and decrease [CO32-] and pH. This process of ocean acidification is expected to cause a drastic change of marine ecosystem composition and a decrease in calcification ability of various benthic invertebrates. The studied area, Kiel Fjord, is characterized by high pCO2 variability due to upwelling of O2 depleted and CO2 enriched bottom water. Within less than 50 years, eutrophication of the Baltic Sea has drastically increased the mean pCO2 in the fjord. The observed increase and also the rate of this acidification process is much higher than it is expected for the global ocean as a consequence of increasing atmospheric CO2 concentrations. In contrast to other areas subjected to elevated pCO2, calcifying invertebrates inhabit Kiel fjord and the benthic community is dominated by the blue mussel Mytilus edulis. Mussel larvae settle in the period of the year when highest pCO2 (800-2300 µatm) are encountered, which is, at the same time, the main growth period due to highest phytoplankton densities. In laboratory experiments, calcification rates of M. edulis are maintained at elevated pCO2 levels which are expected to occur by the year 2300. Only at high pCO2 above 3000 µatm, calcification is significantly reduced. One possible reason for this tolerance is the fact that even under control conditions, the extracellular body fluids (haemolymph and extrapallial fluid, EPF) of M. edulis are characterized by low pH and [CO32-] and high pCO2. Therefore, the EPF which is in direct contact with the shell is undersaturated with calcium carbonate also at current, low seawater pCO2. Under elevated pCO2, mussels do not buffer the extracellular acidosis by means of bicarbonate accumulation. Thus haemolymph pH and [CO32-] are reduced even further. Calcification might not be affected by the extracellular acidosis, as an amorphous calcium carbonate (ACC) precursor is most probably formed in intracellular vesicles. Since mussels are able to efficiently regulate the intracellular pH, reduced extracellular pH might therefore have only little impact on the initial calcification process. On the other hand, the production of the organic shell components, e.g. the periostracum, consumes high amounts of energy. Especially in young thin shelled life stages with a higher organic shell content most of the energy allocated to growth is required for shell production. Under elevated pCO2, mussels initially (two months acclimation) up - regulate their metabolic rates which may indicate higher energy demand for ion regulatory processes. Long-term acclimated animals (12 months acclimation) probably switch to an energetically less expensive compensation and do not exhibit elevated aerobic metabolism. However, long-term acclimated mussels are characterized by lower filtration rates. As consequence, after both intermediate and long-term exposure, the scope for growth is reduced in high pCO2 acclimated animals. Additionally, after intermediate and also long-term acclimation to elevated pCO2, protein metabolism is increased, as indicated by an elevation of ammonia excretion rates. This mode of energy generation is less efficient than oxidation of lipid or carbohydrate and may contribute to lower energy availability for growth and calcification. Similar to other aquatic animals, ammonia excretion in mussels seems to be facilitated by NH3 diffusion through Rhesus (Rh) and ammonium transporter (Amt) protein channels and subsequent acid-trapping by separate proton excretion. In order to test the importance of energy supply and elevated pCO2 on mussel calcification, juvenile M. edulis were exposed to a crossed experimental design for seven weeks. Higher food supply enables mussels to calcify also under highly elevated pCO2. In general food supply is the most important factor which determines the growth rates of mussels whereas pCO2 has only a minor effect. In a simultaneous field study, mussels were transplanted to the energy rich high pCO2 inner fjord and to the outer parts of the fjord at lower pCO2 and particulated organic carbon concentrations. Similar to the laboratory experiment, mussels exhibit much higher growth rates in the high pCO2 inner fjord with its higher particulate organic carbon concentrations. This reveals the importance of energy availability impacting CO2 tolerance of M. edulis. Mussels seem to be relatively tolerant to elevated pCO2 both in laboratory experiments and under current high pCO2 conditions in Kiel Fjord. The high energy availability present in the eutrophicated habitat may support the tolerance to elevated pCO2. In the future, increasing atmospheric CO2 concentrations will drastically elevate pCO2 level in this habitat. The benthic life stages seem to be able to cope with the expected levels but plantonic larvae might be vulnerable. However, M. edulis exhibit a high adaptation potential to the rate of acidification in the recent past and might be able to adapt also to higher levels in future. In order to predict the success of M. edulis in future, also effects of elevated temperature and the response of their main predators to these conditions needs to be considered. Increasing atmospheric CO2 concentrations equilibrate with the surface water of the oceans and thereby increase seawater pCO2 and decrease [CO32-] and pH. This process of ocean acidification is expected to cause a drastic change of marine ecosystem composition and a decrease in calcification ability of various benthic invertebrates. The studied area, Kiel Fjord, is characterized by high pCO2 variability due to upwelling of O2 depleted and CO2 enriched bottom water. Within less than 50 years, eutrophication of the Baltic Sea has drastically increased the mean pCO2 in the fjord. The observed increase and also the rate of this acidification process is much higher than it is expected for the global ocean as a consequence of increasing atmospheric CO2 concentrations. In contrast to other areas subjected to elevated pCO2, calcifying invertebrates inhabit Kiel fjord and the benthic community is dominated by the blue mussel Mytilus edulis. Mussel larvae settle in the period of the year when highest pCO2 (800-2300 µatm) are encountered, which is, at the same time, the main growth period due to highest phytoplankton densities. In laboratory experiments, calcification rates of M. edulis are maintained at elevated pCO2 levels which are expected to occur by the year 2300. Only at high pCO2 above 3000 µatm, calcification is significantly reduced. One possible reason for this tolerance is the fact that even under control conditions, the extracellular body fluids (haemolymph and extrapallial fluid, EPF) of M. edulis are characterized by low pH and [CO32-] and high pCO2. Therefore, the EPF which is in direct contact with the shell is undersaturated with calcium carbonate also at current, low seawater pCO2. Under elevated pCO2, mussels do not buffer the extracellular acidosis by means of bicarbonate accumulation. Thus haemolymph pH and [CO32-] are reduced even further. Calcification might not be affected by the extracellular acidosis, as an amorphous calcium carbonate (ACC) precursor is most probably formed in intracellular vesicles. Since mussels are able to efficiently regulate the intracellular pH, reduced extracellular pH might therefore have only little impact on the initial calcification process. On the other hand, the production of the organic shell components, e.g. the periostracum, consumes high amounts of energy. Especially in young thin shelled life stages with a higher organic shell content most of the energy allocated to growth is required for shell production. Under elevated pCO2, mussels initially (two months acclimation) up - regulate their metabolic rates which may indicate higher energy demand for ion regulatory processes. Long-term acclimated animals (12 months acclimation) probably switch to an energetically less expensive compensation and do not exhibit elevated aerobic metabolism. However, long-term acclimated mussels are characterized by lower filtration rates. As consequence, after both intermediate and long-term exposure, the scope for growth is reduced in high pCO2 acclimated animals. Additionally, after intermediate and also long-term acclimation to elevated pCO2, protein metabolism is increased, as indicated by an elevation of ammonia excretion rates. This mode of energy generation is less efficient than oxidation of lipid or carbohydrate and may contribute to lower energy availability for growth and calcification. Similar to other aquatic animals, ammonia excretion in mussels seems to be facilitated by NH3 diffusion through Rhesus (Rh) and ammonium transporter (Amt) protein channels and subsequent acid-trapping by separate proton excretion. In order to test the importance of energy supply and elevated pCO2 on mussel calcification, juvenile M. edulis were exposed to a crossed experimental design for seven weeks. Higher food supply enables mussels to calcify also under highly elevated pCO2. In general food supply is the most important factor which determines the growth rates of mussels whereas pCO2 has only a minor effect. In a simultaneous field study, mussels were transplanted to the energy rich high pCO2 inner fjord and to the outer parts of the fjord at lower pCO2 and particulated organic carbon concentrations. Similar to the laboratory experiment, mussels exhibit much higher growth rates in the high pCO2 inner fjord with its higher particulate organic carbon concentrations. This reveals the importance of energy availability impacting CO2 tolerance of M. edulis. Die steigenden CO2 Konzentration der Atmosphäre und die folgende Äquilibrierung mit dem Oberflächenwasser der Ozeane führen zu erhöhten pCO2 und sinkenden Karbonationen Konzentrationen ([CO32-]) und pH Werten. Die sogenannte Ozeanversauerung hat vermutlich weitreichende Auswirkungen auf die marinen Ökosysteme und führt möglicherweise dazu, dass die Kalzifizierungsraten insbesondere benthischer Wirbelloser abnimmt. Das Untersuchungsgebiet der Kieler Förde weist, durch den Auftrieb bodennahen Wassers mit niedriger O2 Sättigung und hohen CO2 Konzentrationen, bereits heutzutage hohe und variable pCO2 Werte auf. Innerhalb der letzten 50 Jahre hat die Eutrophierung zu einer deutlichen Erhöhung der pCO2 Werte in der Förde geführt. Damit ist sowohl das Ausmaß als auch die Geschwindigkeit der Versauerung höher, als es für die weltweiten Ozeane im Zuge des zukünftigen CO2 Anstiegs zu erwarten ist. Im Gegensatz zu anderen Gebieten, die vergleichbar erhöhten pCO2 Werten ausgesetzt sind, leben zahlreiche kalzifizierende Wirbellose in der Förde und die Miesmuschel Mytilus edulis dominiert die benthische Gemeinschaft. Die Larven der Muscheln siedeln insbesondere in der Jahreszeit in der die höchsten pCO2 Werte (800-2300 µatm) auftreten. Aufgrund der hohen Phytoplanktonkonzentrationen ist dies ebenfalls die Zeit der höchsten Wachstumsraten. In Laborversuchen ist M. edulis in Lage die Kalzifizierungsraten unter erhöhten pCO2 Werten, die für das Jahr 2300 erwartet werden, aufrechtzuerhalten. Extrazelluläre Flüssigkeiten (Hämolymphe und extrapalliale Flüssigkeit, EPF) weisen auch unter Kontrollbedingungen hohe pCO2 Werte und niedrige pH und [CO32-] auf. Die EPF, die in direktem Kontakt zur Schale steht, ist demnach auch bei niedrigem Meerwasser pCO2 mit Kalziumkarbonat untersättigt. Bei erhöhtem Meerwasser pCO2 säuert sich die Hämolymphe an und wird nicht durch Bikarbonat gepuffert. Die Ansäuerung des extrazellulären Raumes hat vermutlich deshalb nur geringe Auswirkungen auf die Kalzifizierung, da ein amorpher Kalziumkarbonatvorläufer bereits in intrazellulären Vesikeln gebildet wird. Muscheln können den intrazellulären pH weitestgehend unabhängig vom Außenmedium regulieren, weshalb die extrazelluläre Ansäuerung die Schalenbildung nur geringfügig beeinflusst. Allerdings benötigt die Synthese der organischen Schalenbestandteile sehr viel Energie. Insbesondere in jungen, dünnschaligen Lebensstadien, die Schaleen mit einem höheren Organikanteil aufweisen, wird der größte Teil der für das Wachstum benötigten Energie in die Schalenbildung investiert. Unter erhöhtem pCO2, weisen Muscheln zunächst höhere metabolische Raten auf, was möglicherweise auf einen erhöhten Energiebedarf für aktive Ionentransportprozesse hinweist. Nach langer Akklimation scheinen sie auf eine effizientere Regulation zu wechseln und der aerobe Stoffwechsel ist nicht mehr erhöht. Allerdings nimmt die Filtrationsleistung ab. In beiden Fällen ist demnach die Energie, die für das Wachstum zur Verfügung steht, reduziert. Außerdem ist nach mittlerer und Langzeit-Akklimierung der Proteinstoffwechsel erhöht, erkennbar an der höheren Ammoniumexkretion. Diese Art der Energiegewinnung ist weniger effizient als Lipid- und kohlenhydratstoffwechsel und könnte zu einer verminderten Energieverfügbarkeit beitragen. Wie auch in anderen aquatischen Tieren scheint die Ammoniumexkretion in Muscheln durch Rhesus (Rh) und Ammoniumtransporter (Amt) Kanalproteine und eine anschließende Protonierung gefördert zu werden. Die Bedeutung von Energieversorgung und erhöhtem pCO2 auf die Kalzifizerung ist in einem gekreuzten Versuchsansatz getestet worden. Höhere Futterzugabe ermöglicht den Muscheln die Kalzifizierung auch unter hohen pCO2. Generell ist die Futterzufuhr von größerer Bedeutung für das Wachstums während pCO2 nur einen geringen Effekt hat. In einem zeitgleich durchgeführten Feldexperiment sind junge Muscheln in die Innenförde mit ihren hohen pCO2 und in die Außenförde mit niedrigeren pCO2 und partikulären organischen Kohlenstoffkonzentrationen verpflanzt worden. In Übereinstimmung mit dem Laborexperiment, weisen die Tiere in der inneren Förde trotz des höheren pCO2 deutlich höhere Wachstumsraten als die in der Außenförde auf. Dieses Ergebnis betont die Bedeutung der Energieverfügbarkeit für die Toleranz von M. edulis gegenüber der Ozeanversauerung. Muscheln scheinen gegenüber erhöhten pCO2 Werten in Laborexperimenten aber auch innerhalb der Kieler Förde relativ tolerant zu sein. Die hohe Energieverfügbarkeit in dem eutrophierten Habitat der Kieler Förde könnte die Toleranz gegenüber hohen pCO2 Werten fördern. Allerdings werden die steigenden CO2 Konzentrationen der Atmosphäre die pCO2 Werte der Förde zukünftig deutlich erhöhen. Während die benthische Lebensphase gegenüber den erwarteten Werten tolerant zu sein scheint, könnten the planktischen Larven sensibler sein. Allerdings wies M. edulis eine hohe Anpassungsrate an die Versauerung der jüngeren Vergangenheit auf und könnte dementsprechend auch in der Lage sein, sich an zukünftige Bedingungen anzupassen. Um verlässlich vorherzusagen, ob M. edulis auch in Zukunft erfolgreich sein wird, ist es notwendig auch die Effekte erhöhter Temperaturen und die Auswirkungen solcher Bedingungen auf die Haupträuberorgansismen zu berücksichtigen.

Anthropogenic emissions of carbon dioxide (CO2) resulting from fossil fuel burning and changes in land use are affecting our marine environment; for example leading to ocean acidification or ocean warming. In order to understand how climate change will affect biological communities we need to understand all levels of biological responses. Community change as a response to environmental drivers are composed of three components: the physiological responses within an organism, described by its phenotypic plasticity or reaction norm and the ecological and evolutionary responses which are associated with changes on the species and genotype level, respectively. Moreover, there may be eco-evolutionary coupling, thus either ecological interactions such as competition that modify evolutionary responses to physico-chemical changes, or evolutionary change that feeds back to change ecological interactions. Here I study for the first time over the long-term (up to 220 generations) how among two competing phytoplankton species the different response types play out, and whether or not coupling of ecological and evolutionary processes can be found. Additionally I investigated the short-term inter- and intraspecific responses of three phytoplankton species to increased CO2 and what role competitive interactions play on the short-term in a two-species ´community´.

Sea surface temperature (SST) variability within the equatorial Atlantic is of climatic relevance for the surrounding continents. A striking feature of this SST variability is the annual appearance of the Atlantic cold tongue (ACT). The respective contributions to the ML heat budget forming the seasonal cycle of SSTs within the ACT could up to date not be clarified. Especially the role of the diapycnal heat flux due to turbulence in cooling SSTs is still controversially discussed. The main focus of this study is to infer regional and seasonal variability of upper ocean turbulent mixing and the inferred diapycnal heat flux within the ACT region using a multi cruise data set of microstructure observations. The assessed varibility of the diapycnal heat flux is then integrated into the ML heat budget within different regions and seasons of the ACT. In addition, the variability in mixing intensity is related to the variability in large scale background conditions, which were additionally observed during the cruises. The observations indicate fundamental differences in background conditions in terms of shear and stratification below the mixed layer (ML) for the western and eastern equatorial as well as the southern ACT region. This leads to the occurrence of critical Froude numbers (Fr), which points towards elevated mixing intensity, most frequently in the western equatorial ACT. The distribution of critical Fr below the ML reflects the regional and seasonal variability of mixing intensity. Turbulent dissipation rates (ε) at the equator (2°N-2°S) are strongly increased in the upper thermocline compared to off-equatorial locations. In addition, ε is elevated in the western equatorial ACT compared to the east from May to November, whereas boreal summer appears as the season of highest mixing intensities throughout the equatorial ACT region, coinciding with ACT development. Diapycnal heat fluxes at the base of the ML in the western equatorial ACT region inferred from ǫ and stratification range from a maximum of 90 W/m² in boreal summer to 40 W/m² in November. In the eastern equatorial ACT region maximum values of about 25 W/m² were estimated during boreal summer. Outside the equatorial region, inferred diapycnal heat fluxes are comparably low rarely exceeding 10 W/m². Critical to the enhanced diapycnal heat flux in the western equatorial ACT region during boreal summer and autumn is elevated meridional velocity shear in the upper thermocline. It is thus suggested that TIWs are crucial contributors to mixing within this region during this time period. Integrating the obtained heat flux estimates in the ML heat budget accentuates the diapycnal heat flux as the largest ML cooling term during boreal summer and early autumn in the entire equatorial ACT region and crucial for decreasing SSTs for ACT development. Within the southern ACT region SST cooling is dominated by atmospheric forcing. Additionally, it is shown that most of the existing parametrization schemes for the equatorial thermocline, which are supposed to estimate the general magnitude of mixing related parameters without cost-intensive observations, tend to overestimate turbulent mixing intensity and the inferred diapycnal heat fluxes within the equatorial ACT region. Die Variabilität der Meeresoberflächentemperatur (SST) im äquatorialen Atlantik ist von klimatischer Bedeutung für die angrenzenden Kontinente. Ein charakteristisches Merkmal dieser SST Variabilität ist das saisonale Auftreten der atlantischen Kaltwasserzunge (ACT). Die individuellen Beiträge zum Wärmebudget der Deckschicht, das den saisonalen Verlauf der SST bestimmt, konnten bis heute nicht vollständig geklärt werden. Speziell der Beitrag des diapyknischen Wärmeflusses aufgrund von Turbulenz ist noch immer umstritten. Das Hauptziel dieser Arbeit ist die Bestimmung der regionalen und saisonalen Variabilität der turbulenten Vermischung und des resultierenden, diapyknischen Wärmeflusses in den oberen Schichten der ACT Region. Die Basis für diese Untersuchung bildet ein Datensatz von Mikrostrukturbeobachtungen gewonnen während diverser Schiffsreisen in verschiedene Regionen der ACT während unterschiedlicher Jahreszeiten. Die abgeschätzte Variabilität des diapyknischen Wärmeflusses wird dann in das Wärmebudget der Deckschicht integriert. Die daraus bestimmte Variabilität der turbulenten Vermischung wird im Folgenden mit der Variabilität der groß-skaligen Zirkulation in Beziehung gesetzt. Die Beobachtungen der Hintergrundbedingungen in Form der Parameter Scherung und Schichtung unterhalb der Deckschicht lässt fundamentale Unterschiede zwischen der westlichen und östlichen äquatorialen, sowie der südlichen ACT Region erkennen. Dies führt dazu, dass kritische Froude Zahlen (Fr), die ein Indikator für erhöhte Vermischungsintensität sind, am häufigsten in der westlichen äquatorialen ACT Region auftreten. Die Verteilung kritischer Fr Zahlen unterhalb der Deckschicht ist generell in guter Übereinstimmung mit der regionalen und saisonalen Variabilität turbulenter Vermischungsintensität. Dissipationsraten der turbulenten kinetischen Energie (ε) in der äquatorialen Region (2°S-2°N) sind deutlich erhöht verglichen mit polwärtigen Regionen. Außerdem ist ε in der westlichen, äquatorialen ACT Region von Mai bis November höher als im Osten. Die borealen Sommermonate, übereinstimmend mit dem Zeitpunkt des Auftretens der ACT, können als die Saison höchster Vermischungsaktivität innerhalb der gesamten äquatorialen Region identifiziert werden. Diapyknische Wärmeflüsse am Fuße der Deckschicht in der westlichen, äquatorialen ACT Region, abgeleitet aus Beobachtungen von ε und Schichtung, reichen von maximal 90 W/m² im borealen Sommer bis 40 W/m² zu im November. In der östlichen, äquatorialen Region wurden maximal 25 W/m² während des borealen Sommers beobachtet. Außerhalb der äquatorialen Region übersteigen die diapyknischen Wärmeflüsse niemals 10 W/m² . Einen wesentlichen Beitrag zu den hohen Wärmeflüssen in der westlichen, äquatorialen Region vor allem im borealen Sommer und Herbst liefert die meridionale Komponente der Geschwindigkeitsscherung. Es ist deshalb zu vermuten, dass tropische Instabilitätswellen (TIWs), die diese Geschwindigkeitskomponente wesentlich beeinflussen, einen wichtigen Beitrag zur turbulenten Vermischung in dieser Region liefern. Die Integration des abgeschätzten diapyknischen Wärmeflusses in das Wärmebudget der Deckschicht hebt hervor, dass der diapyknische Wärmefluss den größten Beitrag zur Abkühlung im borealen Sommer und Herbst in der gesamten, äquatorialen ACT liefert. Dies betont seine Schlüsselrolle für die Abkühlung während der ACT Entstehung. In der südlichen ACT Region ist das Wärmebudget der Deckschicht hauptsächlich durch atmosphärische Terme bestimmt. Desweitern wird gezeigt, dass existierende Turbulenz-Parametrisierungen für die äquatoriale Region, die eine grobe Abschätzung der relevanten turbulenten Größen ohne kostspielige Messungen ermöglichen sollen, die Vermischungsintensität und die abgeleiteten diapyknischen Wärmeflüsse überschätzen.