Abstract
In order to predict the future fate of the Greenland Ice Sheet, a thorough understanding of both recent and past changes is required. In particular, the importance of the different factors influencing the stability of marine-terminating glaciers needs to be unraveled, since these glacierstransport large amounts of ice from the interior of the Ice Sheet towards the ocean. The rapid acceleration and retreat of marine-terminating glaciers at the start of this century was associated with increased flow of warm, Atlantic-derived waters onto the Greenlandic shelf. This led to the hypothesis that the variable inflow of ocean currents constitutes a major control on the dynamic behavior of large marine outlet glaciers. This thesis investigates marine sediment cores from fjords and bays in West and Southeast Greenland, located near large marine-terminating glaciers. These include paleoceanographic investigations of multi-millenial trends from sediments deposited since the Early Holocene in Køge Bugt, SE Greenland, multi-centennial trends of the last 2000 year in Disko Bugt near Jakobshavn Isbræ in West Greenland, and multi-decadal patterns during the 20th century in Upernavik and Kangerlussuaq Fjord, in respectively Northwest and East Greenland. The variability of ice-rafted debris is measured, together with proxies of oceanic variability (foraminiferal assemblages and Uk’37). From this, the potential impact of oceanic changes on glacier stability prior to the satellite era is examined. Also, the different variables that influence the proxy records are discussed, leading to an improved understanding of their application. Overall, this thesis shows that ocean warming likely has been an important control on the stability of large tidewaters glaciers retreat the Holocene, but that variations in bedrock topography are able to mediate their response. In Køge Bugt, glacier experienced a minimal response to the warm conditions during the Holocene Thermal Maximum, likely as a result of local topography. In Disko Bay, cooling of bottom waters allowed the formation of an ice tongue of Jakobshavn Isbræ between AD 1500-1850, which potentially disintegrated in response to the ocean warming that followed. In Upernavik Fjord and Kangerlussuaq Fjord the inflow of warm, Atlantic-derived waters reflects surface variability in the North Atlantic, and peaked around 1930 and after 2000. These periods were associated with accelerated retreat of Upernavik Isstrøm, and could have triggered the newly-discovered, major collapse of Kangerlussuaq Glacier’s ice shelf between 1932-1933
| Originalsprog | Engelsk |
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| Forlag | Natural History Museum of Denmark, Faculty of Science, University of Copenhagen |
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| Status | Udgivet - 2019 |
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