| Summary: | During present time, the global climate is changing at a rapid pace. To understand the future consequences of these changes, studies of past abrupt climate change are essential. A natural analogue to the current climate change is re-occurring abrupt warming episodes first witnessed in Greenland during the Last Glacial period. These events, referred to as Dansgaard-Oeschger (DO) events manifested as rapid warming on decadal timescales of up to 15°C in Greenland air temperature, followed by a gradual decline to colder temperatures. Understanding of the forcing mechanisms behind these events is currently limited by chronological uncertainties and the inability to accurately synchronize disparate climate records. However, the application of tephrochronology has the potential for testing hypotheses regarding the synchroneity of past climate change events. This by utilizing the near to simultaneous deposition of geochemically distinct tephra material in different climate archives over large geographical distances. That potential is demonstrated in this thesis, by the documentation of previously known and unknown tephra horizons in the North Atlantic Ocean. Findings presented in this thesis extend the established North Atlantic marine tephra framework by the identification of the well-known Faroe Marine Ash Zone (FMAZ) II-1 and North Atlantic Ash Zone (NAAZ) II (II-RHY-1) tephra horizons in the Irminger and Labrador Seas. A significant discovery, opening for a wider marine- marine cross-correlation of paleoproxy records. Furthermore, this thesis demonstrates the previously unknown tephrochronological potential of the Labrador Sea region by the publication of the first continuous tephrostratigraphic record from this area. Here, five isochronous tephra layers sourced from the Bárdarbunga-Veidivötn and Grímsvötn volcanic systems have the potential to serve as important chronological tie- points, if identified elsewhere in future studies. Collectively, these two studies (Paper 1 and 3), document that regions outside the ...
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