ALBERT

Description: This study investigated effects of small-scale turbulence on growth and other selected characteristics of autotrophic planktonic flagellates. Under turbulent conditions generated in the laboratory, experiments in pure batch culture were conducted with Prymnesium parvum (Prymnesiophyceae), Pyrenomonas helgolandii (Cryptophyceae), Prorocentrum redfieldii, Alexandrium minutum, A. fundyense and A. tamarense (Dinoflagellata). Net growth rate of two species were affected by small-scale turbulence, i. e. enhancement in P. parvum, impairment in A. tamarense. In P. redfieldii aggregation and mortality of the cells was enhanced. Except for a slight effect towards smaller cell size in A. tamarense turbulence showed no effect on the size in the six species examined. Carbon and nitrogen content of the cells and their relation were not affected by small-scale turbulence in P. helgolandii and P. redfieldii. The content of chlorophyll a and some accessory pigments was also not affected in the four dinoflagellate species examined. In the three Alexandrium species the cellular contents of mean toxins causing paralytic shellfish poisoning (PSP) were not influenced during the exponential growth stage, but during stagnation and decline, gonyautoxin in A. fundyense increased with increasing turbulence. The effects of small-scale turbulence might also depend on the growth stage of the organisms. Experiments in chemostat cultures instead of batch cultures might be more suitable for investigating the effect of small-scale turbulence in discrete growth stages and are recommended for future experiments.

Description: The newly developed Kiel Climate Model (KCM) is used to study the influence of global warming on the El Nino-Southern Oscillation (ENSO). The global warming scenario used in this study involves increasing the C02 concentration by 1 % per annum until the concentration has doubled and thereafter stabilised. An ensemble of eight global warming simulations were performed. They were compared against a 330 year stable simulation for current climate conditions. In the first step, the simulation of the tropical climate, mean state, ENSO and its dynamics in the control run are assessed by comparing them against observations. In the second step, the changes induced by the global warming scenario in the mean state of tropical Pacific, the simulation of ENSO, and three major ENSO feedbacks are examined. KCM simulates global climate relatively well in terms of mean state, annual cycle, variability, and ENSO. However, like many models, KCM exhibits a 1 °C cold bias in the cold tongue of the equatorial Pacific sea surface temperature (SST), overestimates the variability, underestimates the non-linear effects and is also lacking the typical phase locking to the annual cycle. The simulated global warming scenario is well inside the range of other coupled general circulation models and shows a linear increase in the surface air temperature during the increase of the C02 concentration. The major findings are near uniform warming of the sea surface temperature combined with a deepening and sharpening of the thermocline. These changes in the mean state result in a doubling of the amplitude and an increase in the extreme El Nino events. These changes in the mean state were shown to strengthen feedbacks between thermocline depth and SST and between SST and zonal wind stress, both of these contribute to the increased ENSO variability.

Description: Seismic and volcanic activity in Central Java, Indonesia, is related to the subduction of the Indo-Australian plate beneath the Sunda plate. The MERAMEX project (MERapi AMphibious EXperiments) studied the relationship between subduction zone processes and arc volcanism in Central Java. In 2004, a temporary seismological network was installed and seismic refraction and reflection profiles, bathymetric, gravimetric, and magnetic data was acquired. The airgun signals of the three profiles were recorded both at OBH stations deployed along the seismic profiles and within the onshore receiver array. The reflection and refraction data of the three seismic profiles were forward modelled and the P-wave velocity information was used to generate background velocity models for the tomographic calculations. Tomographic inversions of the active onshore data were performed using the 3DTH (Hole 1992) and LOTOS-06 (Koulakov et al. 2007) codes. The onshore active data and local earthquakes were also jointly inverted using LOTOS-06. The tomographic models show a low-velocity structure aligned in a NNE-SSW direction that separates the rigid forearc into two blocks. The hypocenter of the May 26, 2006 Java magnitude Mw=6.4 earthquake and its aftershocks are concentrated along the eastern edge of this elongated low-velocity zone. An anomalously-strong low-velocity anomaly is located in the backarc crust just north of the volcanoes Sumbing, Merapi and Lawu. The velocity perturbations, the attenuation of P- and S- waves, the high Poisson’s ratio of 0.3, its correlation with a gravity low and the location in the active Sunda Arc, all suggest that the low-velocity anomaly is caused by multiple magma reservoirs and ascending feeder systems below the volcanoes of Central Java.

Description: Detailed bathymetric mapping of the area of 15°N (MAR) as well as geological mapping of the Logatchev hydrothermal field at 14°45´N (MAR) leads to a very well description of the Logatchev hydrothermal field and adjacent areas. Main parts of the Logatchev hydrothermal field are located in a depression filled with talus material and pelagic sediment this causes an increase in porosity and permeability in the subseafloor influencing fluid pathways importantly and provide aquifers wherein fluids can spread out laterally in layers of mafic/ultramafic talus. The ‚smoking craters‛ of the Logatchev hydrothermal field are rare structures which have only been identified at Logatchev and the, in 2005 newly discovered, Nibelungen-Field at the southern MAR (Koschinsky at al., 2006). Bathymetric maping of the seafloor reveal that the hydrothermal activity at Logatchev mainly is fault controlled. The Logatchev hydrothermal field is characterized by five smoking craters, two hydrothermal mounds with black smokers and a couple of diffuse vent sites. The smoking craters emanate fluids with temperatures up to ~350°C. Host Rocks of the field are mainly serpentinites (〉70%) and gabbroic rocks (〉20%) with subordinately basalt. Serpentinites, gabbroic rocks, and altered sediments were sampled from the active ultramafic hosted Logatchev hydrothermal field (LHF) by ROV deployments and TV-guided grab. In this study we present new data of clay-size separates and whole rock chemistry as well as strontium and oxygen isotopic compositions in order to investigate the alteration processes, water-rock reactions and associated elemental exchanges. The samples of mantle peridotites are mostly serpentinized (〉95 vol%) whereas some gabbroic samples are moderately to completely altered. Changes in geochemical compositions, especially trace element compositions, of the altered rocks indicate a highly heterogeneous distribution of alteration styles. Light rare earth elements are enriched in all serpentinites and suggest a strong influence of Logatchev vent fluids during some stages of serpentinization. Oxygen isotopic data of lizardites reveal formation temperatures of 130-150°C whereas chlorite formation in altered gabbroic samples occurred between 150° and 200°C in the LHF. Negative as well as positive Eu anomalies in serpentinites suggest varying alteration processes: (1) high temperature alteration in acidic, reducing conditions as well as (2) low temperature alteration in neutral, oxidizing environments. The absence of brucite and the formation of talc indicate high concentrations of aquatic silica in the Logatchev area. Petrographic investigations, high field strength element data and elevated rare earth elements indicate that melt–rock interaction is also an important factor affecting mantle peridotite prior to serpentinization processes at LHF. Therefore gabbroic intrusions are the most probable source for aquatic silica. Strontium isotopic data suggest high water/rock ratios in the range of 2.6-27 and alteration fluids which are characterized by high contents of heated seawater.Calculations of relative gains and losses of major and trace elements as well as mineralogical observations reveal that a large variety of alteration styles take place at the Logatchev hydrothermal field. A combination of serpentinization, hydrothermal fluids, melt-rock interaction and low-temperature seafloor weathering lead to significant gains and losses of major and trace elements. We found that serpentinization at Logatchev was isochemical for the most major elements (excepting a loss of TiO2 and CaO). However, the concentration of trace elements e.g., Cu, Nb, Ba, La, Sm, Eu, Th or U increases strongly in the serpentinites. In addition, gabbroic intrusions are a sink for MgO during the formation of chlorite and serpentine after clinopyroxene and play a major role as distributors of SiO2, TiO2, CaO, and Na2O as well as numerous trace elements in the circulating fluids.

Description: Within the framework of this thesis investigations on formation and dissolution processes of Mg-calcites have been carried out. Based on the results of mineralogical and isotope geochemical investigations it was possible to reconstruct the formation processes of authigenic high Mg-calcite concretions sampled from mud mounds of the Costa Rica forearc. Furthermore, based on laboratory work, the oxygen isotope fractionation of high Mg-calcite in aqueous media was examined. Finally, dissolution experiments on CaMg-carbonates were performed and theoretic kinetic parameters could be defined for the dissolution processes. Chapter I presents a short introduction describing the natural occurrence of Mg-calcites and their formation processes. Furthermore, different experimental techniques, which are applied to investigate precipitation- and dissolution processes of carbonates, are introduced. Formation processes of authigenic carbonates in Mounds 11 and 12 (Costa Rica forearc) are discussed in Chapter II. The pore water geochemical profiles from sediment cores collected in the study area show the active diagenetic processes leading to carbonate mineral precipitation. Investigation of the stable carbon and oxygen isotope composition of the collected authigenic concretions indicates a complex formation scenario, possibly controlled by sediment erosion, varying fluxes of methane-rich fluid, and thus migration zones of carbonate formation. Based on the stable isotope composition of the authigenic concretions and the respected geochemical pore fluid composition a common deep fluid source is postulated for the two mud mounds. The third chapter investigates the effect of Mg2+ incorporation on the oxygen isotope fractionation of high Mg-calcite in the temperature range between 25 and 80oC. Synthetic high Mg-calcites with various MgCO3 content are prepared in the laboratory from oversaturated solutions with respect to calcite. A new technique for the separation of crystalline from amorphous carbonate was developed. The results, including a new expression for the Mg-calcite-water oxygen isotope fractionation, imply that the incorporation of Mg2+ in the calcite crystal lattice has a much bigger effect on the Mg-calcite - water oxygen isotope fractionation, than it was previously defined by laboratory precipitation experiments at 25°C. The new isotope fractionation factor (this study) rather fits to recently published thermodynamic calculations, and will help to improve our knowledge about the environmental conditions during natural Mg-calcite formation. The investigation of CaMg-carbonate dissolution in aqueous media is presented in the fourth chapter. The run of the concentration vs. time curves could be fitted by a simple kinetic equation. Kinetic constants controlling the equation were determined and are comparable to previously published data. Furthermore, experiments performed in distilled water showed that dissolution rates of authigenic (13%)Mg-calcite are comparable to dissolution rates of calcite, when the geometric surface is used in the kinetic equation. In the case of dissolution experiments in NaCl solutions (0.6M), with ionic strength similar to seawater, the solvent obviously strongly determines the reaction order and dissolution rate of Mg-calcite. It is believed that the presented results could be used to improve the existing diagenetic models describing diagenetic dissolution/precipitation processes of CaMg-carbonates in e.g. cold seep areas.

Description: The focus of this study is to explore the long term Plio-Pleistocene variability of coastal and open ocean upwelling systems by reconstructing for the last ~3.5 Ma, sea surface temperature (SST), primary productivity and nutrient cycling in the Benguela Upwelling System (BUS) and the Eastern Equatorial Pacific (EEP), two areas particularly sensible and influential to climate change.

Description: Planktonic foraminifera from tropical Atlantic and Caribbean sediment-surface samples (0-1 cm) show general westward-directed increasing calcification depths depending on the east-west increase in thermocline depth. Positively related planktonic foraminiferal Mg/Ca and carbonate ion concentration in the Caribbean show well preserved Mg/Ca down to depths about 1.5 km above the lysocline, which equals a carbonate ion concentration of 26-18 µmol/kg. Species-specific calibrations of Mg/Ca with d18O-derived calcification temperatures reveal similar exponential and differing preexponential constants for shallow- and thermocline-dwelling compared to deep-dwelling species. For multispecies, a "warm water" and a "cold water" calibration was derived. Alteration of deep-sea sediments in the vicinity of the Bahama platform results in micro-scale inorganic crystallites on planktonic foraminiferal tests, which synchronize the absence of high Mg-calcite from the sediments. Mg/Ca and Sr/Ca of the crystallites are 4-6 times elevated and 2-3 times depleted, respectively, compared to the original foraminiferal test.

Description: Most active marine electromagnetic surveys use an array of transmitting and receiving electric dipoles located on the sea-floor. There are many reports of successful detections of buried resistors with these arrays. Nevertheless, the concept has a significant drawback: Large offsets between the transmitter and receiver with respect to the target depth are needed. A logical alternative is the use of a vertical electric-dipole transmitter in a borehole deeper than the target, combined with receivers located at the seafloor. Because current must pass through the target, even data recorded at short offsets with respect to target depth should be sensitive to the target. We derived the equations for the electric and magnetic field components produced by the vertical electric dipole in a 1D layered medium. The equations are used to model the fields for resistive layers. An eigenparameter analysisis applied to the different field components, and the resolution is compared with the standard seafloor inline array. The analyses show that data for the downhole transmitter are more sensitive to the resistance between the source and the receiver than the sea-floor array. However, model geometry such as depth to the target is resolved less easily. The resolution of the model geometry is improved significantly when a long bipole transmitter is used, extended from below the target layer to a level above it. We carried out 3D modeling for the downhole transmitter through the use of a finite-difference algorithm. Results indicate that these data are very sensitive to lateral changes within the target layer. Differences between electric fields simulated at the seafloor for 3D models and a reference model show a correlation to lateral resistivity differences. This finding suggests that the array is suitable for mapping and monitoring resistivity anomalies outward from the borehole.

Description: Dieser Artikel diskutiert den Charakter von Pollentypen. Wir argumentieren, dass Pollentypen und Pflanzentaxa komplett unterschiedliche Entitäten (morphologische bzw. taxonomische) sind, und deswegen unterschiedlich behandelt und dargestellt werden sollten. Allgemeine Probleme der konventionellen Nomenklatur von Pollentypen werden anhand von Beispielen aus der europäischen palynologischen Praxis illustriert. Wir plädieren für Deutlichkeit in der Nomenklatur von Pollentypen und für die wissenschaftliche Freiheit, ‘unkonventionelle‘ Methoden zu benutzen, um Verwirrung zu vermeiden.

Description: research