ALBERT

Description: One of Earth’s most fundamental climate shifts – the greenhouse-icehouse transition 34 Ma ago – initiated Antarctic ice-sheet build-up, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7–33.2 Ma) that immediately followed this transition, a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization, is uncertain. Here, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin – a key region for understanding Antarctic ice sheet-evolution. These data indicate a cool-temperate environment, with mild ocean and air temperatures preventing West Antarctic Ice Sheet formation. Climate-ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change.

Description: This paper introduces SEISMONOISY, an application designed for monitoring the spatiotemporal characteristic and variability of the seismic noise of an entire seismic network with a quasi-real-time monitoring approach. Actually, we have applied the developed system to monitor 12 seismic networks distributed throughout the Italian territory. These networks include the Rete Sismica Nazionale (RSN) as well as other regional networks with smaller coverage areas. Our noise monitoring system uses the methods of Spectral Power Density (PSD) and Probability Density Function (PDF) applied to 12 h long seismic traces in a 24 h cycle for each station, enabling the extrapolation of noise characteristics at seismic stations after a Seismic Noise Level Index (SNLI), which takes into account the global seismic noise model, is derived. The SNLI value can be used for different applications, including network performance evaluation, the identification of operational problems, site selection for new installations, and for scientific research applications (e.g., volcano monitoring, identification of active seismic sequences, etc.). Additionally, it aids in studying the main noise sources across different frequency bands and changes in the characteristics of background seismic noise over time.

Description: Published

Description: 3474

Description: JCR Journal

Description: Based on its morphology and in accordance with modern circumscriptions of genera among the Gleicheniaceae, a new combination in Sticherus is made for the Papua New Guinean fern originally described as Gleichenia hooglandii.

Description: This Doctorial Thesis investigates the fundamental problem of flow and deposition processes of unsteady, inertial flows of granular media and elucidates its implications for the behaviour of pyroclastic flows formed in explosive volcanic eruptions. A three-fold approach is followed including laboratory experiments, their theoretical analysis, and field work on the pristine pyroclastic flow deposits of the 1975 eruption of Mt. Ngauruhoe (New Zealand). The experiments are based upon the physical problem of the sudden collapse of vertical columns of granular media onto a base and their subsequent spreading behaviour. Through investigations of the pyroclastic flow deposits of the 1975 eruption of Mt. Ngauruhoe, first complete data sets of the internal structure and grain-size distribution and the morphology of the upper free surface of small-volume pyroclastic flow deposits as a function of travel distance, underlying slope and topographic confinement are presented. This detailed data set is interpreted using the experimental findings on the propagation of an internal interface, and a qualitative time- and space-dependent model on transport, segregation and deposition is developed for pyroclastic flows.

Description: Die vorliegende Arbeit untersucht, inwieweit die Photonenweglängenverteilung der durch Wolken transmittierten solaren Strahlung Informationen über die Wolkeneigenschaften enthält und sich damit zur Wolkenfernerkundung eignet. Hierzu wurden Photonenweglängen (PPL) mit dem rückwärts rechnenden Monte-Carlo-Strahlungstransportmodell MC-UNIK-BW für dreidimensional inhomogene Wolkenfelder aus hydrodynamischen Modellläufen des mesoskaligen Atmosphärenmodells GESIMA simuliert. Die stärkste Korrelation der mittleren PPL mit den 13 untersuchten Wolkeneigenschaften liegt für die optische Dicke der Wolken vor. Relativ unabhängig von dieser Beziehung zeigt sich die Verbindung der PPL zur internen Wolkeninhomogenität. Der Einfluss der Inhomogenität zeigte sich auch in dem Vergleich zwischen einer gemessenen und einer modellierten PPL. Des Weiteren stellt sich heraus, dass ein existierender Zusammenhang zwischen der PPL und den Wolkeneigenschaften für einen größeren horizontalen Bereich der Wolken Gültigkeit behält. Durch die Aufspaltung des Datensatzes an PPL-Simulationen in unterschiedliche Messsituationen ergaben sich neue Korrelationen mit zum Teil deutlichen Verbesserungen der Korrelationen im Vergleich zum gesamten Datensatz. Daneben wurde auch der Einfluss der Gasabsorption auf die resultierende PPL und die Änderung der PPL mit der Variation des Messortes in einem Wolkenfeld untersucht.

Description: Highlights • All investigated sites are in quiescent stage. Multi layers of clam shell debris were the ancient sediment surfaces during high methane flux. • Current fluxes contribute to less than 2 wt % of authigenic carbonates and 2 wt % iron sulfide minerals being precipitated in 600-800 cm sediment. • The sequestration of carbon could be 〉 50 mmol C cm-2 yr-1 under current in situ condition. Abstract Methane seepage records information of the local carbon cycle with respect to the generation, consumption and sequestration of carbon. Here presents the investigation of 7 gravity cores retrieved in 2004 during cruise SO-177 in the Haiyang 4 Area at the northern slope of the South China Sea. Porewater solutes, sulfate, methane, total alkalinity, sulfide and calcium demonstrate currently the weak seep activity. Local carbon cycling and sequestration is also revealed, that dominates by anaerobic oxidation of biogenic methane to dissolved bicarbonate inducing calcium carbonate and iron sulfide minerals (mainly pyrite) precipitation. A reactive transport model was employed to quantify the carbon cycle and budget. Model results show that current methane fluxes contribute to less than 2 wt % of authigenic carbonates and 2 wt % iron sulfide minerals being precipitated in 600–800 cm sediment depth. The sequestration of carbon could be 〉 50 mmol C cm−2 yr−1 under in situ condition. The observed increase of carbonate and iron sulfide minerals at ∼100 cm, however, require higher methane fluxes to shift the zone of anaerobic oxidation of methane upwards to around 1 m below the seafloor, which have occurred during sea level low stands in the geological past. The oscillation of seepage flux contributed to the formation of multiple layers of authigenic carbonates and pyrite, which indicates the high capability of carbon sink and is speculated to be induced by the dissociation of the underlying hydrates triggered by sea level drop and or temperature increase.

Description: Wolken spielen im globalen Wasser- und Energiekreislauf eine bedeutende Rolle. Ständig sind rund 66% der Erde von Wolken bedeckt. Der Bedeckungsgrad variiert auf saisonalen, interannualen und interdekadischen Zeitskalen. In dieser Diplomarbeit soll neben der saisonalen Variabilität der Bedeckung auch die interannuale und interdekadische Variabilität des Bedeckungsgrades in einem gekoppelten Atmosphäre/Ozean Zirkulationsmodell ECHAM5/NEMO untersucht werden. Im weiteren werden Wechselwirkungen zwischen dem Bedeckungsgrad und anderen Klimavariablen (SST, Bodenluftdruck, Niederschlag) betrachtet. Im ersten Teil (Kapitel 5 und 6) der vorliegenden Arbeit wird zur Validierung der Modelldaten eine Vergleichsstudie mit globaler Wolkenbedeckung aus Satellitenbeobachtungen des International Satellite Cloud Climatology Project (ISCCP) durchgeführt. Die globale Verteilung der Gesamtbedeckung im Modell folgt entsprechend den Beobachtungsdaten der für die verschiedenen Klimazonen typischen Verteilung. Es zeigen sich jedoch lokale Differenzen. So ist die globale Gesamtbedeckung im Model global um 2,46% höher als beobachtet. Die Gesamtbedeckung in den Tropen, Subtropen und Teilen der mittleren Breiten wird vom Modell unterschätzt, in den subpolaren und polaren Breiten wird diese vom Modell überschätzt. Die saisonale Variabilität des Bedeckungsgrades wird vom Modell verstärkt wiedergegeben. Diese Unterschiede wurden auch in anderen Vergleichsstudien zwischen modellierter Bedeckung in GCMs und Satellitendaten gefunden. Der zweite Teil (Kapitel 7) dieser Diplomarbeit beschreibt Korrelationsanalysen zwischen dem Bedeckungsgrad und der SST sowie dem Bodenluftdruck. Anhand dieser Korrelationsanalysen werden Aussagen über gemeinsame Variabilitäten getroffen. Ziel ist es, Wechselwirkungen aufzuzeigen. Im Vergleich zwischen modellierter und beobachteter SST zeigen sich Abweichungen von bis zu 6 K. Ein Vergleich von Korrelationen zwischen Bedeckungsgrad und SST sowohl mit Modelldaten als auch mit Beobachtungsdaten zeigt jedoch, dass die Haupkorrelationsmuster vom Modell wiedergegeben werden. Jedoch können aufgrund der gröberen Auflösung im Modell kleinskalige Wechselwirkungen nicht im Detail wiedergegeben werden. Neben der SST nimmt der Bodenluftdruck starken Einfluss auf die Wolkenbedeckung. Muster hoher Korrelationen stimmen jedoch nur bedingt mit der klimatologischen Verteilung des Bodenluftdrucks und seinen Drucksystemen (Hochdruckgebiete, Tiefdruckgebiete) überein. Im dritten Teil (Kapitel 8) dieser Arbeit wird die Variabilität der Wolkenbedeckung auf verschiedenen vertikalen Leveln im Zusammenhang mit der Variabilität der Oberflächentemperatur und dem Bodenlufdruck untersucht. So kann gezeigt werden, dass Rahmenbedingungen am Boden wie Luftdruck und Temperatur mit Wolken in unterschiedlichen Höhen unterschiedlich stark wechselwirken. Im weiteren wird deutlich, dass sich der Anteil der Variabilität des Gesamtbedeckungsgrades aus Variabilitäten in unterschiedlichen Höhen und somit unterschiedlichen Wolkentypen zusammensetzt. Im letzten Teil (Kapitel 9 und 10) werden Rückkopplungen zwischen dominanten Mustern regionaler Klimavariabilität, ENSO und NAO, in Hinblick auf die Variabilität des Bedeckungsgrades untersucht.

Description: This diploma thesis analyses the negative change of the SST in the midlatitude on the north hemisphere in spring and summer, which has a connection to the atmospherical condition. The SST rise with incident solar radiation in spring and summer, so that the ocean mixed layer becomes thinner and warmer. And than the SST decreases about 0.5 Kelvin or more in 6 till 48 hours. This temperature subsidence can only explained with the mixing of the ocean mixed layer with colder water from below the mixed layer. When it comes from a atmospherical general conditions, this intermixture arise with the impaced of the wind.The wind stress transmits moment on the ocean and stimulate Ekman circulation and Langmuir circulation. The analyse base on data from a coupled run of the atmosphere circulation model ECHAM with the ocean model Mopy. The wind data and the data of the geopotentical high is used for the analyse. It is analysed in which atmospherical situation a negative change of the SST existed. The hypothesis is that a low in the midlatitude have a connection to the negative change of the SST. To show this, different statistical methods are used. The negative SST change exist in the area between the subtropical high and the lows in the midlatitude. A direct relationship between the SST change and the atmosphere is only found at the wind speed. The wind speed must increase clear compared with the wind speed of the time before. If the wind speed increases, the SST can decrease 0.5 Kelvin or more to the following time. When negative SST change exists, the mean of the wind speed is higher then the mean of the wind speed at all areas and time points. The comparison of the geopotentical height in 1000hPa level doesn't show a typical situation in which the negative SST change exist. The wind speed arises in different areas of a low and also in a high. On the other hand there is a relationship between negative SST change and geopotentical height in 500hPa level. The negative SST change exists often with eopotentical height in 500hPa level which is greater than the mean, that means in the subtropical air respectively is connected with a ridge. The polar front is connected with the ground over the dynamic lows in the midlatitude. The ridge belongs to ridge of high pressure and the warm section of a low. Between the ridge and the trough is the cold front at the ground. After the cold front the trough comes in the high level. The wind speed is weak in the high, so the ocean mixed layer can become thinner and warmer. When the low comes near, the wind speed becomes stronger and the ocean mixed layer is mixed with colder water. So the SST decreases and a negative SST change arises.

Description: This thesis shows different aspects of the distribution of zooplankton and the resulting influence on larval fish survival. The vertical distribution of the key calanoid copepod species in the Bornholm Basin (Baltic Sea), Pseudocalanus acuspes (Giesbrecht 1881), Temora longicornis (Müller 1792), Acartia bifilosa (Giesbrecht 1882), Acartia longiremis (Lilljeborg 1853) and the only cyclopoid copepod Oithona similis (Claus 1863), were investigated. Sampling was carried out with multiple opening/closing nets. The results showed distinct seasonal differences in the vertical distribution for all species. For P. acuspes an ontogenetic migration was detected, with the younger stage dwelling near the surface and the older stages moving successively deeper. The adults inhabited the water layers around the halocline. In November the vertical distribution disintegrated and all stages were distributed over the whole water column. However in this period the older stages (C4, C5) dominated the community. A diel vertical migration was observed for T. longicornis in the summer month (June 2001, July and August 2002). The migration was most distinc for the older stages, moving from 20 metre at night to almost 60 metre at day. No diel migration was observed in April and November. For Acartia species an extended daily migration was not observed, even though the weighted mean depth of Acartia longiremis in July shifted from 10 metre at night to 20 metre at day. Both Acartia species inhabited the water column above the thermocline in spring and summer. However, in November the distribution was broader for all stages in both species. All stages of O. similis inhabited the water layers around the halocline irrespective to the season, showing no vertical migration. The distribution of reproducing female P. acuspes was investigated with the Video Plankton Recorder, an in situ imaging device. The distribution was closely related to high salinity although low oxygen values were avoided. Based on images of female P. acuspes carrying egg sacs the number of eggs per clutch was calculated and using the temperature dependent development time an in situ egg production rate was estimated. Albeit the production was the same between years, the naupli to female ratio was higher in 2003 leading to the conclusion that the naupli mortality might have been reduced. A simple individual based model of P. acuspes connected to a circulation model of the Baltic Sea was used to reveal possible influence of drift to biomass changes. The results showed that in contrast to the 1980’s during the 1990’s the prevailing barotrophic circulation forced the majority of P. acuspes out of the Bornholm Basin into easterly Basins and shallow coastal regions. However, the transport of organisms produced in the eastern Basins (Gotland Basin and Gdansk Deep) back to the Bornholm Basin was limited. Lower salinity and higher temperature in the near shore water might influence the survival and reproduction. The same circulation model was used to investigate the drift of larval cod and possible consequences on the overlap with food organisms. Again, a shift in the baroclinic circulation between the 1980’s to the 1990’s led to an increased dispersion of larvae in the latter period. It was shown that this decreased the overlap with larval prey and thus decreased the survival probability of larval cod. Furthermore, the influence of variability in prey abundance and diversity on the results of an individual based model on larval cod growth and survival was investigated. It was shown, that the use of idealized mean prey fields led to an overestimation of larval survival. Using field data derived from net sampling the survival was partly reduced to 50%. Another investigated factor was the size of prey organisms. Again, the use of mean value led to an overestimation of survival. Using measurements from samples reduced the survival up to 75%.

Description: An advection-diffusion model coupled to a simple dynamical ocean model is used to illustrate the formation and ventilation of an oxygen minimum zone. The advection-diffusion model carries a tracer mimicking oxygen, and the dynamical model is a non-linear 1 ½ layer reduced-gravity model. The latter is forced by an annually oscillating mass flux confined to the near-equatorial band that, in turn, leads to the generation of mesoscale eddies and latitudinally alternating zonal jets at higher latitudes. The model uses North Atlantic geometry and develops a tracer minimum zone remarkably similar in location to the observed oxygen minimum zone in the Eastern Tropical North Atlantic (ETNA). This is despite the absence of wind forcing and the shadow zone predicted by the ventilated thermocline theory. Although the model is forced only at the annual period, the model nevertheless exhibits decadal and multidecadal variability in its spun-up state. The associated trends are comparable to observed trends in oxygen within the ETNA oxygen minimum zone. Notable exceptions are the multi-decadal decrease in oxygen in the lower oxygen minimum zone, and the sharp decrease in oxygen in the upper oxygen minimum zone between 2006 and 2013.