@phdthesis{Zamagni2009,
  author    = {Zamagni, Jessica},
  title     = {Responses of a shallow-water ecosystem to the early Paleogene greenhouse environmental conditions : evolution of Larger Foraminifera and coral communities from the Northern Tethys},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-31853},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {Modern anthropogenic forcing of atmospheric chemistry poses the question of how the Earth System will respond as thousands of gigatons of greenhouse gas are rapidly added to the atmosphere. A similar, albeit nonanthropogenic, situation occurred during the early Paleogene, when catastrophic release of carbon to the atmosphere triggered abrupt increase in global temperatures. The best documented of these events is the Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma) when the magnitude of carbon addition to the oceans and atmosphere was similar to those expected for the future. This event initiated global warming, changes in hydrological cycles, biotic extinction and migrations. A recently proposed hypothesis concerning changes in marine ecosystems suggests that this global warming strongly influenced the shallow-water biosphere, triggering extinctions and turnover in the Larger Foraminifera (LF) community and the demise of corals. The successions from the Adriatic Carbonate Platform (SW Slovenia) represent an ideal location to test the hypothesis of a possible causal link between the PETM and evolution of shallow-water organisms because they record continuous sedimentation from the Late Paleocene to the Early Eocene and are characterized by a rich biota, especially LF, fundamental for detailed biostratigraphic studies. In order to reconstruct paleoenvironmental conditions during deposition, I focused on sedimentological analysis and paleoecological study of benthic assemblages. During the Late Paleocene-earliest Eocene, sedimentation occurred on a shallow-water carbonate ramp system characterized by enhanced nutrient levels. LF represent the common constituent of the benthic assemblages that thrived in this setting throughout the Late Paleocene to the Early Eocene. With detailed biostratigraphic and chemostratigraphic analyses documenting the most complete record to date available for the PETM event in a shallow-water marine environment, I correlated chemostratigraphically for the first time the evolution of LF with the δ¹³C curves. This correlation demonstrated that no major turnover in the LF communities occurred synchronous with the PETM; thus the evolution of LF was mainly controlled by endogenous biotic forces. The study of Late Thanetian metric-sized microbialite-coral mounds which developed in the middle part of the ramp, documented the first Cenozoic occurrence of microbially-cemented mounds. The development of these mounds, with temporary dominance of microbial communities over corals, suggest environmentally-triggered "phase shifts" related to frequent fluctuations of nutrient/turbidity levels during recurrent wet phases which preceding the extreme greenhouse conditions of the PETM. The paleoecological study of the coral community in the microbialites-coral mounds, the study of corals from Early Eocene platform from SW France, and a critical, extensive literature research of Late Paleocene - Early Eocene coral occurrences from the Tethys, the Atlantic, the Caribbean realms suggested that these corals types, even if not forming extensive reefs, are common in the biofacies as small isolated colonies, piles of rubble or small patch-reefs. These corals might have developed 'alternative' life strategies to cope with harsh conditions (high/fluctuating nutrients/turbidity, extreme temperatures, perturbation of aragonite saturation state) during the greenhouse times of the early Paleogene, representing a good fossil analogue to modern corals thriving close to their thresholds for survival. These results demonstrate the complexity of the biological responses to extreme conditions, not only in terms of temperature but also nutrient supply, physical disturbance and their temporal variability and oscillating character.},
  language  = {en}
}
@phdthesis{Mueller2022,
  author    = {M{\"u}ller, Daniela},
  title     = {Abrupt climate changes and extreme events in two different varved lake sediment records},
  doi       = {10.25932/publishup-55833},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-558331},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVIII, 209},
  year      = {2022},
  abstract  = {Different lake systems might reflect different climate elements of climate changes, while the responses of lake systems are also divers, and are not completely understood so far. Therefore, a comparison of lakes in different climate zones, during the high-amplitude and abrupt climate fluctuations of the Last Glacial to Holocene transition provides an exceptional opportunity to investigate distinct natural lake system responses to different abrupt climate changes. The aim of this doctoral thesis was to reconstruct climatic and environmental fluctuations down to (sub-) annual resolution from two different lake systems during the Last Glacial-Interglacial transition (~17 and 11 ka). Lake Gościąż, situated in the temperate central Poland, developed in the Aller{\o}d after recession of the Last Glacial ice sheets. The Dead Sea is located in the Levant (eastern Mediterranean) within a steep gradient from sub-humid to hyper-arid climate, and formed in the mid-Miocene. Despite their differences in sedimentation processes, both lakes form annual laminations (varves), which are crucial for studies of abrupt climate fluctuations. This doctoral thesis was carried out within the DFG project PALEX-II (Paleohydrology and Extreme Floods from the Dead Sea ICDP Core) that investigates extreme hydro-meteorological events in the ICDP core in relation to climate changes, and ICLEA (Virtual Institute of Integrated Climate and Landscape Evolution Analyses) that intends to better the understanding of climate dynamics and landscape evolutions in north-central Europe since the Last Glacial. Further, it contributes to the Helmholtz Climate Initiative REKLIM (Regional Climate Change and Humans) Research Theme 3 "Extreme events across temporal and spatial scales" that investigates extreme events using climate data, paleo-records and model-based simulations. The three main aims were to (1) establish robust chronologies of the lakes, (2) investigate how major and abrupt climate changes affect the lake systems, and (3) to compare the responses of the two varved lakes to these hemispheric-scale climate changes. Robust chronologies are a prerequisite for high-resolved climate and environmental reconstructions, as well as for archive comparisons. Thus, addressing the first aim, the novel chronology of Lake Gościąż was established by microscopic varve counting and Bayesian age-depth modelling in Bacon for a non-varved section, and was corroborated by independent age constrains from 137Cs activity concentration measurements, AMS radiocarbon dating and pollen analysis. The varve chronology reaches from the late Aller{\o}d until AD 2015, revealing more Holocene varves than a previous study of Lake Gościąż suggested. Varve formation throughout the complete Younger Dryas (YD) even allowed the identification of annually- to decadal-resolved leads and lags in proxy responses at the YD transitions. The lateglacial chronology of the Dead Sea (DS) was thus far mainly based on radiocarbon and U/Th-dating. In the unique ICDP core from the deep lake centre, continuous search for cryptotephra has been carried out in lateglacial sediments between two prominent gypsum deposits - the Upper and Additional Gypsum Units (UGU and AGU, respectively). Two cryptotephras were identified with glass analyses that correlate with tephra deposits from the S{\"u}phan and Nemrut volcanoes indicating that the AGU is ~1000 years younger than previously assumed, shifting it into the YD, and the underlying varved interval into the B{\o}lling/Aller{\o}d, contradicting previous assumptions. Using microfacies analyses, stable isotopes and temperature reconstructions, the second aim was achieved at Lake Gościąż. The YD lake system was dynamic, characterized by higher aquatic bioproductivity, more re-suspended material and less anoxia than during the Aller{\o}d and Early Holocene, mainly influenced by stronger water circulation and catchment erosion due to stronger westerly winds and less lake sheltering. Cooling at the YD onset was ~100 years longer than the final warming, while environmental proxies lagged the onset of cooling by ~90 years, but occurred contemporaneously during the termination of the YD. Chironomid-based temperature reconstructions support recent studies indicating mild YD summer temperatures. Such a comparison of annually-resolved proxy responses to both abrupt YD transitions is rare, because most European lake archives do not preserve varves during the YD. To accomplish the second aim at the DS, microfacies analyses were performed between the UGU (~17 ka) and Holocene onset (~11 ka) in shallow- (Masada) and deep-water (ICDP core) environments. This time interval is marked by a huge but fluctuating lake level drop and therefore the complete transition into the Holocene is only recorded in the deep-basin ICDP core. In this thesis, this transition was investigated for the first time continuously and in detail. The final two pronounced lake level drops recorded by deposition of the UGU and AGU, were interrupted by one millennium of relative depositional stability and a positive water budget as recorded by aragonite varve deposition interrupted by only a few event layers. Further, intercalation of aragonite varves between the gypsum beds of the UGU and AGU shows that these generally dry intervals were also marked by decadal- to centennial-long rises in lake level. While continuous aragonite varves indicate decadal-long stable phases, the occurrence of thicker and more frequent event layers suggests general more instability during the gypsum units. These results suggest a pattern of complex and variable hydroclimate at different time scales during the Lateglacial at the DS. The third aim was accomplished based on the individual studies above that jointly provide an integrated picture of different lake responses to different climate elements of hemispheric-scale abrupt climate changes during the Last Glacial-Interglacial transition. In general, climatically-driven facies changes are more dramatic in the DS than at Lake Gościąż. Further, Lake Gościąż is characterized by continuous varve formation nearly throughout the complete profile, whereas the DS record is widely characterized by extreme event layers, hampering the establishment of a continuous varve chronology. The lateglacial sedimentation in Lake Gościąż is mainly influenced by westerly winds and minor by changes in catchment vegetation, whereas the DS is primarily influenced by changes in winter precipitation, which are caused by temperature variations in the Mediterranean. Interestingly, sedimentation in both archives is more stable during the B{\o}lling/Aller{\o}d and more dynamic during the YD, even when sedimentation processes are different. In summary, this doctoral thesis presents seasonally-resolved records from two lake archives during the Lateglacial (ca 17-11 ka) to investigate the impact of abrupt climate changes in different lake systems. New age constrains from the identification of volcanic glass shards in the lateglacial sediments of the DS allowed the first lithology-based interpretation of the YD in the DS record and its comparison to Lake Gościąż. This highlights the importance of the construction of a robust chronology, and provides a first step for synchronization of the DS with other eastern Mediterranean archives. Further, climate reconstructions from the lake sediments showed variability on different time scales in the different archives, i.e. decadal- to millennial fluctuations in the lateglacial DS, and even annual variations and sub-decadal leads and lags in proxy responses during the rapid YD transitions in Lake Gościąż. This showed the importance of a comparison of different lake archives to better understand the regional and local impacts of hemispheric-scale climate variability. An unprecedented example is demonstrated here of how different lake systems show different lake responses and also react to different climate elements of abrupt climate changes. This further highlights the importance of the understanding of the respective lake system for climate reconstructions.},
  language  = {en}
}