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Title: Constraining rapid climate transitions in the North Atlantic using tephrochronology
Author: Griggs, Adam James
ISNI:       0000 0004 7425 4935
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2015
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Abrupt climatic transitions that characterise the Late Pleistocene are recognised in a number of palaeoarchives, yet little has advanced our understanding of the causal mechanisms. High-resolution atmospheric changes are best represented in the Greenland ice-core records and North Atlantic marine sediments preserve a sequence of oceanic responses during these rapid events. An understanding of forcing mechanisms, however, is currently hampered by chronological uncertainties and an inability to integrate proxy records from these different realms. Tephrochronology is one of the few techniques that offer the potential to establish independent and precise tie-points between marine and ice-core records. Four marine sequences are explored to assess the potential of utilising tephra and cryptotephra deposits as time-synchronous marker horizons during Marine Isotope Stage 2 and 3. Tephras preserved in the marine environment are subjected to a range of secondary transportation and depositional processes, such as iceberg rafting and bioturbation, as well as primary airfall. Using a range of diagnostic indicators, a protocol is proposed to i) assess the processes controlling tephra deposition ii) to inform isochron placement and iii) to identify primary deposits that can act as valuable marker horizons. Moreover, a pioneering application of thin-section and Xray microtomography analyses are presented to assist in the assessment of postdepositional processes. These techniques highlight some of the complexities of marine tephrochronology and the possibilities they offer for fully resolving depositional integrity. Through application of this protocol, ten primary tephra deposits are identified and together form a marine tephrochronological framework for the North East Atlantic region. Four deposits are new discoveries and augment the volcanic event stratigraphy and enhance the number of isochrons available for synchronisation. Geochemical characterisation and stratigraphical analysis are employed to assess the presence of coeval marine and ice-core horizons. Two ice-marine tie-lines, FMAZ II and NAAZ II, have been successfully utilised to identify the relative timing of climatic events and highlight the potential of synchronising records. Some of the challenges of correlating marine deposits to the Greenland ice-cores are explored, and recommendations are made for future applications of marine tephrochronology.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available