Forwick, Matthias
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Item type:Publication, Unraveling the Chukchi Shelf sediments: insights into past ice sheet extent and gas migration(2023-12-15); ; ; Marine geophysical methods are utilized to image sedimentary deposits on shelf areas and continental slopes, offering insights into permafrost existence, gas migration, and the historical dynamics of ice sheets. This study focuses on the depositional history of outer Chukchi Shelf sediments and adjacent Chukchi Borderland, investigating glacial periods' impact on the sea floor, specifically a potential ice sheet along the Beringia continental margin. Reprocessed seismic data from 2011, part of a tectonic study on the Chukchi Shelf, reveals a glacial unconformity and distinctive seafloor structures indicative of multiple ice masses. Along the Beringian margin, varying thicknesses of glacial deposits, reaching 450m in certain areas, hint at the extent of an ice sheet and ice stream dynamics. Additionally, seismic data highlights migration structures of rising methane, suggesting its release into the water column, though typical gas seepage surface features are absent. The absence of large-scale marine permafrost on the Chukchi Shelf is indicated by seismic velocities. Overall, these findings provide crucial information for further geological exploration of this previously understudied continental margin, shedding light on its glacial history and potential methane outgassing.doctoral thesis244 130 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Sea-ice dynamics along West Antarctic continental shelves from the last deglacial to the Holocene - A multi-proxy biomarker approach(2024-05-03); ; ; After experiencing three record-breaking low sea-ice summers in a course of seven years, Antarctic sea ice prompts a gaining interest among climate researchers. It is now more important than ever to get the best possible understanding of past Antarctic sea-ice behavior and its response to long- and short-term atmospheric and oceanographic changes on regional and pan-Antarctic scales. The knowledge as well as newly collected data will improve model simulations that aim to predict the future development of this climate-sensitive feature. Therefore, the need for tools that allow consistent and reliable paleo-reconstructions of Southern Ocean sea ice is high. The recently introduced organic sea-ice biomarker proxy IPSO25 has the potential to fulfill this need, however, thorough assessments of its applicability hitherto are sparse. A suite of sediment samples from West Antarctic continental shelves, which are affected most by strongly negative sea-ice trends, were investigated within this thesis to evaluate the proxy’s potential to display the recent and past sea-ice coverage in the study areas. A study on seafloor surface sediments from the West Antarctic Peninsula, the Amundsen and Weddell seas demonstrated that the IPSO25 concentrations within the sediments do not adequately reflect the recent sea-ice conditions derived from satellite and numerical model data. For a semi-quantitative estimation of the sea-ice cover, IPSO25 was combined with a phytoplankton marker, resulting in the sea-ice index PIPSO25 (analogous to the sea-ice index IP25 for the Arctic), that allows are more realistic estimate of sea-ice coverage and hence seems to be a more suitable tool for paleo sea- ice reconstructions. To gather more information on ocean temperature, measurements of isoprenoidal glycerol dialkyl glycerol tetraethers were carried out and compared to instrument measurements of sea surface and subsurface temperatures, revealing the general capability of the proxy to mirror ocean temperatures. In a further study, the applicability of IPSO25 alongside phytoplankton biomarkers, the sea-ice index PIPSO25, sedimentological parameters and physical properties was further investigated by means of a high-resolution sediment core located in the direct vicinity of the Pine Island Glacier in the eastern Amundsen Sea Embayment. Here, the multi-proxy dataset revealed the evolution from a polynya setting towards a more sea- ice dominated regime during the early Holocene and a following build-up of a heavy sea-ice cover. Potential interconnections between the regional sea-ice conditions and the inflow of Circumpolar Deep Water onto the continental shelf were drawn and discussed. For the third study as part of this thesis, IPSO25, phytoplankton biomarkers, the sea- ice index PIPSO25 and sedimentological proxies were used for sea-ice reconstructions in the western Amundsen Sea and compared to winter sea ice-estimates based on diatom assemblages. The multi-proxy dataset documents the waxing and waning of the Getz Ice Shelf since the last deglaciation. The first break-up of the Getz Ice Shelf around 13 cal. ka BP and the establishment of a sea-ice cover was followed by a phase of significantly reduced sea-ice cover at around 12.7 cal. ka BP until a re-expansion of sea ice occurred throughout the Holocene. These developments were linked to interhemispheric climate patterns. Regarding the new findings collected within this thesis, IPSO25 and the PIPSO25 approach can be considered a promising tool for (paleo) sea-ice reconstructions on the continental shelves off West Antarctica when interpreted carefully and alongside other paleoenvironmental parameters.doctoral thesis152 143 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Shallow sedimentary structures on the eastern part of the Lomonosov Ridge(2022-09-09); ; ; Während zweier Forschungsfahrten mit dem Forschungsschiff Polarstern in den Jahren 2014 und 2018 wurden bathymetrische, sedimentecholot- und reflexionsseismischen Daten vom östlichen Teil des Lomonossow-Rückens aufgenommen. Die Datensätze kartieren den östlichen Lomonossow-Rücken flächig und lassen nur kleine Lücken im Untersuchungsgebiet. Basierend auf diesen Datensätzen präsentiere ich neue Erkenntnisse über die Topographie und die Struktur der flachen Sedimente des Rückens. Ich leite daraus Prozesse und Ereignisse ab, die die heutige Morphologie des Rückens prägten. Meine Ergebnisse zeigen einen Rücken mit mehreren submarinen Hangrutschungen an beiden Flanken des Lomonossow-Rückens. Sie kommen häufig auf dem Rücken vor, sind aber im Vergleich zu weltweit existierenden submarinen Hangrutschungen klein. Obwohl die flachste Stelle im Untersuchungsgebiet 719 m unter dem heutigen Meeresspiegel liegt und der Rücken im Vergleich zu anderen Kontinentalrändern keine Eiseinzugsgebiete aufweist, konnte ich submarine glaziale Strukturen bis zu einer Wassertiefe von 1250 m nachweisen. Diese Ergebnisse bestätigen, dass der Bergrücken einst von einer bis zu 1250 m dicken Eismasse erodiert wurde. Die Daten zeigen allerdings auch nicht-erodierte Gebiete in Wassertiefen flacher als 1000 m. Diese Beobachtungen deuten auf eine Eismasse mit regional unterschiedlicher Mächtigkeit hin, die von weniger als 1000 m bis zu 1250 m dicke reichte. Meine Untersuchungen zur Sedimentstruktur des Lomonossow-Rückens deuten auf ein normales Absinken des Rückens nach seiner Abspaltung von der Barents-Kara-See hin. Dies steht im Gegensatz zu anderen Hypothesen, die eine Hebung nach seiner Abspaltung oder eine Verzögerung seiner Absenkung vorschlagen. Diese Hypothesen wurden vorgeschlagen, um die Ergebnisse der Arctic Coring Expedition (ACEX) zu erklären, ein 428 m langer Sedimentkern gezogen auf dem zentralen Lomonossow-Rücken. Dessen Sedimentaufzeichnungen zeigen einen 26 Millionen Jahre langen Hiatus im mittleren Känozoikum, sowie Sedimente, die in flachen Gewässern abgelagert wurden, direkt unter und über dem Hiatus. In dieser Arbeit erörtere ich vier Faktoren, die den Hiatus während einer normalen Absenkung des Lomonossow-Rückens verursacht haben könnten.doctoral thesis235 142