Kasemann, Simone
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Kasemann, Simone
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Kasemann, Simone
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Kasemann, Simone Antonia
Kasemann, Simone A.
Kasemann, S. A.
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Item-typ:Veröffentlichung, Impact of melt water controlled material flux on the sedimentation in the western Baffin Bay and the circum-Greenland marginal seas(2023-06-08); ; ; The Arctic is highly sensitive to present climate change and is known to be affected by higher degrees of warming than any other region. Since the Arctic is strongly linked to the global climate system by atmospheric and oceanic circulations, it is crucial to learn more about present and possible future environmental changes in the region. Ice sheets, ice caps, and glaciers play an important role in the Arctic system. To learn more about their sensitivity to climate change, the reconstruction of past ice sheet deglaciation patterns is a helpful tool. An interesting research area for ice sheet reconstruction is the Baffin Bay, which is located between Greenland and the Canadian Arctic and connects the Arctic Ocean with the Labrador Sea. Provenance studies on marine sediments from western Baffin Bay can provide insight into past changes in sediment supply and transport pathways and thus give valuable information about regional ice sheet dynamics and palaeoceanographic conditions. This study analyzed the radiogenic Sr, Nd, and Pb isotope composition of the detrital sediment fraction of four sediment cores from western and northern Baffin Bay and the Canadian Arctic Archipelago. Overall, the data of the sediment cores provide new details on the late Pleistocene and Holocene deglaciation history of the Laurentide Ice Sheet and Innuitian Ice Sheet and related changes in sediment transport processes in western and northern Baffin Bay. Further, the identification of changing sediment provenance of detrital material in marine sediment cores from northern Baffin Bay and Barrow Strait helped to determine better the timing of the opening of these Arctic gateways and the inflow of Arctic waters into Baffin Bay.Dissertation197 188 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Reconstruction of Ediacaran to Early Cambrian ocean pH and weathering conditions(2014-08-08); ; ; This dissertation deals with the reconstruction of ocean pH conditions and the quantification of weathering rates by boron and strontium isotope analyses on Ediacaran and Early Cambrian marine carbonate rocks. In order to compare local signals and specific features with global patterns, a variety of sections on two different palaeo continents (China, Kazakhstan) were examined and compared to data from the Namibian Congo craton. The entire Ediacaran and Early Cambrian was characterized by minor to major ocean pH fluctuations and a general increase in weathering rates and fluxes to the ocean. Ocean acidification events are indicated for the aftermath of the Marinoan glaciation as well as for the Precambrian-Cambrian boundary. The changes in ocean pH and weathering rates had a significant influence on ocean geochemistry and may have decisively contributed to the creation of new ecological niches, possibly enabling the appearance of multicellular animals and reinforcing their radiation.Dissertation553 231 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Holocene ice sheet dynamics and detrital provenance shifts along the West Greenland Margin recorded by radiogenic isotopes (Sr, Nd, Pb)Due to the effect of Arctic Amplification the Arctic is currently warming at least twice as fast as the rest of the planet. Seasonal sea-ice extent has been alarmingly declining in the past decade. Glaciers and ice caps along the Greenland coast and in the Canadian Arctic have been losing mass on an accelerated rate during the past century. As the global climate system is a complex system connecting different regions via atmospheric transport, changes in Arctic climate patterns are affecting the climate and weather conditions in the lower latitudes. The Greenland Ice Sheet as well as glaciers and ice caps in the Canadian Arctic are the largest freshwater storages on the northern hemisphere and expected to be among the highest contributors to global sea level rise. Freshwater input through meltwater discharge is not only affecting sea level rise but further influencing deep water formation in the Labrador Sea and the subpolar North Atlantic and hence global ocean circulation and climate patterns. To be able to sufficiently predict future developments of the Greenland Ice Sheet with respect to mass loss and resulting impacts on the global climate, data from past climate and Greenland Ice Sheet extents are crucially important. The Holocene spanning the last period of the deglaciation after the Last Glacial Maximum culminating in the Holocene Thermal Maximum when atmospheric temperatures were warmer and glacier and ice-sheet extent smaller than today represents the closest analogue to current atmospheric warming and Greenland Ice Sheet mass loss. The wide west Greenland shelf of Baffin Bay and Labrador Sea hosts thick marine sediments archiving around ten thousand years of this past climate and ice-sheet history. Siliciclastic detrital material discharged into Baffin Bay and the Labrador Sea via meltwater and erosion can be separated from those sedimentary archives and traced back to its source region. Radiogenic isotopes (Sr, Nd, Pb) label the source regions of those sediments by fingerprinting the isotopic composition of the prevailing bedrock. Hence, they can be used as reliable provenance tracers. Retreating land-ice masses expose bedrock that before was not subject to erosion, influencing the isotopic signatures delivered into the surrounding ocean. Based on this theory, radiogenic isotopes can record changes in siliciclastic detrital sediment provenance and hence, indirectly trace ice-sheet dynamics. The overall aim of this thesis work is to reconstruct changes in detrital sediment provenance along the west Greenland shelf to gain new insights into Holocene Greenland Ice Sheet dynamics and ocean current-induced sediment transport. Sedimentary archives from three main research areas (eastern Labrador Sea, northeastern Baffin Bay, and Kane Basin, central Nares Strait) record obvious shifts in sediment provenance throughout the Holocene. Those shifts coincide with major regional climatic changes in the research area. Generally, all records reveal the local bedrock as the main source region of detrital material and distal-sourced material transported along the coast via the West Greenland Current as a secondary source. Although the proportion of distal sourced material appears to be small, changes in West Greenland Current strength have been recorded in the isotopic composition. In southwestern Greenland and the Labrador Sea radiogenic isotope records reveal a shift towards a higher proportion of the local Archean Block in the late Holocene caused by Neoglacial ice advance and a reduction in West Greenland Current speed delivering less material from southern most Greenland. Farther north in the Upernavik region, midwest Greenland coast, the isotopic composition marks a change with the transition from early to mid Holocene caused by increased West Greenland Current strength and the opening of Vaigat Strait which enabled erosion and transport of freshly exposed basalts from the Disko Bay area due to ice-sheet retreat. This basalt input is, however, not transported all the way to northernmost Melville Bay (northern Baffin Bay) where the detrital sediment composition is clearly dominated by contribution of the local Committee-Melville Belt without any significant provenance changes throughout the Holocene. Farthest north, the sedimentary record from Kane Basin records provenance shifts that confirm the opening of Nares Strait around 8.3 ka BP. This event is followed by an increased delivery of carbonate-rich detrital sediments from northern Ellesmere Island due to the newly established gateway of Arctic Ocean water transporting sediments from further north to the core location. Additionally determined mineralogical composition of the sedimentary records along the west Greenland coast supports the interpretation drawn from the radiogenic isotopic composition. Furthermore, it points out the additional value of radiogenic isotopes through variations only visible in isotopic composition but not in the mineralogical composition. Further comparison to other studies from the region based on different tracers confirms the reliability and sufficient application of radiogenic isotopes in provenance studies as well as the advantage of multi-proxy approaches in paleoclimatological studies. Overall, this study highlights the advantages and reliability of radiogenic isotopes in provenance studies with regards to reconstructions of ice-sheet dynamics. The combination of the three isotopic systems (Sr, Nd, Pb) enables source region determination with a higher probability compensating for overlapping signatures within individual isotopic systems. The transect of sedimentary records along the west Greenland coast identifies clearly distinguishable isotopic ranges for the different Greenland bedrock terrains, qualifying this approach for further high-resolution investigation in past Greenland Ice Sheet development.Dissertation427 290 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, New Insights into Environmental Conditions for the Early Jurassic (Pliensbachian-Toarcian) from Boron, Lithium and Magnesium Isotopes(2020-06-05); ; ; Das frühe Jura (Pliensbach-Toarc, vor ca. 183 Millionen Jahren (Ma)) zeichnet sich durch einige der drastischsten Umweltkatastrophen des Mesozoikums aus. Die Pliensbach-Toarc Grenze und das im frühen Toarc auftretende Ozeanische Anoxische Event (T-OAE) sind beide von globalem Aussterben und einschneidenden Änderungen der Faunengemeinschaft geprägt. Die biologische Krise beider Events hängt mit dem Auftreten der magmatischen Großprovinz Karoo-Ferrar zusammen, bei dem sehr große Mengen an Magma und Kohlenstoffdioxid (CO2) zutage gefördert wurden. Dies führte zu CO2 Konzentrationen die 2- bis 4-fach höher liegen als noch vor der industriellen Revolution. Die Auswirkungen solch hoher CO2 Konzentrationen waren vielfältig: Erhöhte Temperaturen in der Atmosphäre sowie im Meereswasser, der Verlust von Sauerstoff von großen Teilen des Ozeans, das Auftreten einer möglichen Ozeanversauerung, sowie gravierende Änderungen im Nährstoffkreislauf. Die Kombination dieser vier genannten Stressfaktoren wird auch "Tödliches Quartett" genannt und dessen Vorkommen konnte schon zusammen mit einigen Massenaussterbeevents unserer geologischen Vergangenheit beobachtet werden. Die Menschheit erfährt momentan dieselben Stressfaktoren, die zur Verschlechterung des Klimas und der Umwelt führen, ebenfalls ausgelöst durch den schnellen Anstieg des Treibhausgases CO2 in der Atmosphäre. Allerdings sind heute das Verbrennen des fossilen Brennstoffs und massive Änderungen der Landnutzung der Auslöser dafür. Da die Auswirkungen des raschen CO2 Anstiegs auf das marine Ökosystem noch nicht vorausgesagt werden können, untersuchen wir mit dieser Studie das vergangene T-OAE Event um herauszufinden, welchen Einfluss ein Teil der Stressfaktoren des „Tödlichen Quartetts“ auf das Massenaussterben hatte. Wir geben erste direkte Nachweise für das Auftreten einer Ozeanversauerung während des T-OAE als unmittelbare Folge des schnellen Anstiegs von CO2. Außerdem untersuchen wir die Reaktion des Feedback-Mechanismus der Erde in Form von Silikatverwitterung, das dazu führt, dass der überschüssige CO2 Gehalt aus der Atmosphäre gezogen wird um das natürliche Gleichgewicht wieder herzustellen.Dissertation351 247