ALBERT

Description: Wissenschaftliche Untersuchungen haben gezeigt, dass einige invasive Arten bzw. Populationen gegenüber Umweltstress robuster sind als nicht invasive Arten bzw. Populationen derselben Art. Es wird vermutet, dass die Toleranz gegenüber abiotischen Stressoren wahrscheinlich eine Schlüsseleigenschaft von invasiven Arten darstellt. Während des Transports von Individuen in einen neuen Lebensraum oder durch Stressereignisse könnten widrige abiotische Bedingungen eine Selektion stresstoleranter Individuen hervorrufen, was die erhöhte Stresstoleranz von invasiven Arten bzw. Populationen erklären könnte. Um dies zu testen, habe ich in einem Laborexperiment ein Transport- bzw. Stressereignis simuliert. In zwei unabhängigen Experimenten habe ich in einer Gruppe von Individuen der Weißbeingarnele Penaeus vannamei durch erhöhte Temperaturen mindestens 50 % Mortalität erzeugt. Hierbei wurden die Individuen in unabhängigen Replikaten für 13 Tage 37°C (Langzeit-Stressexperiment) bzw. für 2 h 41°C (Kurzzeit-Stressexperiment) Wassertemperatur ausgesetzt. Nach dieser ersten Stressphase wurde ein Teil der überlebenden gleichzeitig mit einer gleichen Anzahl an bis dahin nicht vorgestressten Individuen sofort wieder denselben erhöhten Temperaturen ausgesetzt und die Überlebenskurven in beiden Gruppen verglichen. Den übrigen überlebenden der ersten Stressphase wurde vor der zweiten Stressphase eine 13 Tage (Langzeit-Stressexperiment) bzw. 6 Tage (Kurzzeit-Stressexperiment) lange Erholungsphase gewährt, damit etwaige physiologische Anpassungen an Stressbedingungen abklingen konnten. Der Vergleich der Überlebenskurven einer vorgestressten Gruppe, die nach der ersten Stressphase direkt wieder Stressbedingungen ausgesetzt wurde und einer vorgestressten Gruppe, der eine Erholungsphase gewährt wurde, sollte Aufschluss darüber geben, ob eine mögliche erhöhte Stresstoleranz der vorgestressten Gruppen auf eine Selektion stresstoleranter Individuen oder physiologischer Anpassungen an Stressbedingungen zurückzuführen war. In beiden Experimenten zeigten die vorgestressten Gruppen, unabhängig davon, ob ihnen eine Erholungsphase gewährt wurde oder nicht, stets höhere Überlebensraten als die Gruppen, die nicht vorgestresst waren. Meine Ergebnisse legen einerseits nahe, dass es durch Temperaturstress zu einer physiologischen Stressabhärtung und dadurch zu erhöhten Überlebensraten der vorgestressten Individuen kam. Da Literaturdaten darauf hinweisen, dass die Erholungsphasen wahrscheinlich lang genug waren, um die physiologische Stressabhärtung in den vorgestressten Gruppen, denen eine Erholungsphase gewährt wurden, abklingen zu lassen, kann man andererseits annehmen, dass es durch den Temperaturstress bei P. vannamei zu einer Selektion stresstoleranterer Individuen gekommen ist. Dies konnte im Rahmen meiner Diplomarbeit jedoch nicht direkt bewiesen werden.

Description: Modeling of the seepage history of DNAPLs is investigated as a new, non-invasive site investigation tool in order to elucidate the possible position of still unknown DNAPL source zone at many investigated industrial sites. Therefore, the spatio-temporal spreading behavior of the DNAPL TCE is studied with the multiphase modeling software TMVOC in small and large scale 2D multiphase scenarios with varying parameter sets concerning groundwater flow, composition of aquifers and aquitards and subsurface morphologies, as depressions and trenches. The small scale models were calibrated by laboratory experiments conducted at La Sapienza University, Rome. They exhibited that even groundwater pore velocities of vw = 0.05 m/d have a strong impact on the spreading behavior and the position of a DNAPL body. Downstream inclined percolation path ways, enhanced dissolution rates and lateral transportation in downstream direction are the most dominant impacts. Small scale layering of the subsoil with horizontal lenses of impermeable materials affects the distribution pattern only slightly at vw 〉 5 m/d, which are common flow velocities in many gravelly aquifers in Europe. Upscaling of the models to field scale problems exhibited potential transportation length in downstream direction of several hundreds of meters, assuming a moderate spill rate of ca. 3 kg/day over an area of several square meters. Investigating real subsurface morphology including real material parameters provided by the ModelPROBE reference site Chimica di Bianchi in Rho, Italy, revealed that the DNAPL TCE will be transported out of moderate depressions (slope of 2.5°) even at groundwater flow velocities of vw ≤ 1 m/d, which is in the range of documented groundwater flow velocities at the reference site. Moreover, the documented material classes, which comprise the aquitard at the site, are not in general impermeable for percolating DNAPLs. Only pure clays with a hydraulic conductivity of kf ≤ 10-9 m/s are long-term barriers for vertical DNAPL percolation. The conducted investigations deliver a reasonable explanation for the often unknown position of DNAPL source zones at former industrial sites and are, as far as it is known, the first large scale scenarios of DNAPL spreading behavior in real subsurface morphology. Based on the conducted research it can be concluded that at the reference site Chimica di Bianchi the main mass of DNAPLs was not at the assumed hot spot, which was encapsulated in the 1980s, but probably migrated considerable distances in downstream direction, passing through or following partly the topography of the aquitard. But the applicability of multiphase modeling as additional non-invasive site investigation tool is still challenging due to software restriction concerning size and resolution of the models and handling of heterogeneous permeability fields.

Description: The isotopic composition of Phanerozoic marine sediments provides important information about changes in seawater chemistry. In particular, the radiogenic strontium isotope (87Sr/86Sr) system is a powerful tool for constraining plate tectonic processes and their influence on atmospheric CO2 concentrations. However, the 87Sr/86Sr isotope ratio of seawater is not sensitive to temporal changes in the marine strontium (Sr) output flux, which is primarily controlled by the burial of calcium carbonate (CaCO3) at the ocean floor. The Sr budget of the Phanerozoic ocean, including the associated changes in the amount of CaCO3 burial, is therefore only poorly constrained. Here, we present the first stable isotope record of Sr for Phanerozoic skeletal carbonates, and by inference for Phanerozoic seawater (δ88/86Srsw), which we find to be sensitive to imbalances in the Sr input and output fluxes. This δ88/86Srsw record varies from ∼0.25‰ to ∼0.60‰ (vs. SRM987) with a mean of ∼0.37‰. The fractionation factor between modern seawater and skeletal calcite Δ88/86Srcc-sw, based on the analysis of 13 modern brachiopods (mean δ88/86Sr of 0.176±0.016‰, 2 standard deviations (s.d.)), is -0.21‰ and was found to be independent of species, water temperature, and habitat location. Overall, the Phanerozoic δ88/86Srsw record is positively correlated with the Ca isotope record (δ44/40Casw), but not with the radiogenic Sr isotope record ((87Sr/86Sr)sw). A new numerical modeling approach, which considers both δ88/86Srsw and (87Sr/86Sr)sw, yields improved estimates for Phanerozoic fluxes and concentrations for seawater Sr. The oceanic net carbonate flux of Sr (F(Sr)carb) varied between an output of -4.7x1010mol/Myr and an input of +2.3x1010mol/Myr with a mean of -1.6x1010mol/Myr. On time scales in excess of 100Myrs the F(Sr)carb is proposed to have been controlled by the relative importance of calcium carbonate precipitates during the “aragonite” and “calcite” sea episodes. On time scales less than 20Myrs the F(Sr)carb seems to be controlled by variable combinations of carbonate burial rate, shelf carbonate weathering and recrystallization, ocean acidification, and ocean anoxia. In particular, the Permian/Triassic transition is marked by a prominent positive δ88/86Srsw-peak that reflects a significantly enhanced burial flux of Sr and carbonate, likely driven by bacterial sulfate reduction (BSR) and the related alkalinity production in deeper anoxic waters. We also argue that the residence time of Sr in the Phanerozoic ocean ranged from ∼1Myrs to ∼20Myrs.

Description: IODP Expedition 307 made it for the first time possible to investigate the entire body of a cold-water coral carbonate mound. Here we provide new insights into the long-term history of Challenger Mound on the European continental margin off Ireland. This study is based on age determinations (230Th/U, 87Sr/86Sr) and geochemical signals (Mg/Li and Ba/Ca) measured in the scleractinian cold-water coral Lophelia pertusa from IODP Site 1317 in the Porcupine Seabight. The paleoceanographic reconstructions reveal that coral growth in the Porcupine Seabight was restricted to specific oceanographic conditions such as enhanced export of primary production and Bottom-Water Temperatures (BWT) between ∼8–10 °C, related to the water mass stratification of the Mediterranean Outflow Water (MOW) and Eastern North Atlantic Water (ENAW). The geochemical signals from the coral skeletons can be explained by the close interaction between cold-water coral growth, sea-surface productivity and the surrounding water masses - the boundary layer between MOW and ENAW. Enhanced sea-surface productivity and the build-up of a stable water mass stratification between ENAW and MOW caused enhanced nutrient supply at intermediate water depths and facilitated a steady mound growth between∼3.0 - 2.1 Ma. With the decrease in sea-surface productivity and related reduced export productivity the food supply was insufficient for rapid coral mound growth between∼1.7 - 1 Ma. During the late Pleistocene (over the last∼0.5 Myr) mound growth was restricted to interglacial periods. During glacials the water mass boundary between ENAW/MOW probably was below the mound summit and hence food supply was not sufficient for corals to grow.

Description: The aragonitic skeletons of scleractinian cold-water corals can serve as valuable archives in paleoceanographic studies. The potential of δ88/86Sr, Sr/Ca, Mg/Ca, Li/Ca and Mg/Li ratios of the cold-water coral Lophelia pertusa to record intermediate water mass properties has been investigated. Here we used samples from several locations along the European continental margin spanning a large temperature range from 6 to 14 °C. Stable strontium isotope measurements were carried out with the recently developed double spike TIMS technique and our results differ from those obtained with less precise methods. In contrast to the strong positive relationship with temperature of previous studies, our results suggest that δ88/86Sr measured in scleractinian cold-water corals is not controlled by seawater temperature, but reflects the Sr isotopic composition of seawater with an offset of Δ88/86Sr = − 0.196‰. As found in previous studies, the elemental ratios Sr/Ca, Li/Ca and Mg/Li measured in corals are significantly related to water temperature and do not correlate with salinity. Moreover, Sr/Ca ratios in L. pertusa display the expected inverse correlation with temperature. However, the variance in the Sr/Ca data severely limits the accuracy of paleotemperature estimates. The Li/Ca and Mg/Ca ratios reveal other influences besides temperature such as pH and/or growth or calcification rate. However, corresponding Mg/Li ratios in L. pertusa are more tightly related to temperature as they remove these secondary effects. In particular, the Mg/Li ratio in L. pertusa may serve as a new promising paleotemperature proxy for intermediate water masses. Our dataset represents the most extensive geochemical examination of L. pertusa to date, revealing a temperature sensitivity of 0.015 mol/mmol/°C for Mg/Li. However, using this temperature dependence and the precision of 5.3% (2SD) only temperature variations larger than ~ 1.5 °C can be resolved with 95% confidence.

Description: The increasing pCO2 in seawater is a serious threat for marine calcifiers and alters the biogeochemistry of the ocean. Therefore, the reconstruction of past-seawater properties and their impact on marine ecosystems is an important way to investigate the underlying mechanisms and to better constrain the effects of possible changes in the future ocean. Cold-water coral (CWC) ecosystems are biodiversity hotspots. Living close to aragonite-undersaturation, these corals serve as living laboratories as well as archives to reconstruct the boundary conditions of their calcification under the carbonate system of the ocean. We investigated the reef-building CWC Lophelia pertusa as a recorder of intermediate ocean seawater pH. This species-specific field calibration is based on a unique sample set of live in-situ collected L. pertusa and corresponding seawater samples. These data demonstrate that uranium speciation and skeletal incorporation for azooxanthellate scleractinian CWCs is pH dependent. However, this also indicates that internal pH up-regulation of the coral does not play a role in uranium incorporation into the majority of the skeleton of L. pertusa. This study suggests L. pertusa provides a new archive for the reconstruction of intermediate water mass pH and hence may help to constrain tipping points for ecosystem dynamics and evolutionary characteristics in a changing ocean.