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Extent, dynamics, and timings of glaciation in the Wicklow Mountains, Ireland, during the Last Glacial-Interglacial Transition

Student thesis: Doctoral Thesis

The focus of this thesis is former ice mass extent and evolution in the Wicklow Mountains, Ireland, during the Last Glacial-Interglacial Transition (LGIT; ~20–10 ka). Whilst previous research has established the existence of a local ice cap, confluent with the wider British-Irish Ice Sheet (BIIS) at the Last Glacial Maximum (LGM; ~24 ka BP), the nature of ice mass recession during the LGIT and subsequent glacier regrowth during the Younger Dryas (YD; 12.9–11.7 ka) requires evaluation. This thesis aims to produce the first regional assessment of the local palaeoglaciological record. The results of systematic geomorphological mapping, based on a combination of remote sensing and field techniques, are presented in the form of the first glacial geomorphological map of the Wicklow Mountains. The post-LGM evolution of local ice is examined based on an assessment of the geomorphological record, establishing the extent, style, and evolution of LGIT mountain glaciation during deglaciation. Using morphostratigraphic principles, two distinct phases of glaciation are recognised; (1) marginal cirque glaciation during the YD, and (2) sub-stages of more extensive topographically-restricted mountain glaciation earlier in the LGIT.
A conservative approach based on an assessment of topographic setting, geomorphology, and radiation modelling indicates that the region hosted six small YD cirque glaciers. The glaciers had an average size of 0.39 km2 and covered a total area of 2.33 km2, based on their reconstruction using a combination of geomorphology and surface profile modelling. Reconstructed ELAs (Area-Altitude Balance Ratio; AABR 1.9 ± 0.81) range from 467 ± 9 m to 739 ± 8 m, with a regional average of 621 ± 9 m. Glacier-derived palaeoprecipitation calculations imply wetter conditions than at present. However, topoclimatic modelling demonstrates that local glacier mass balances were augmented by the redistribution of snow by wind and avalanching, and topographic shading, which artificially lowered ELAs. These processes were essential for marginal YD glacier initiation and survival.
The style and pattern of wider LGIT ice recession is also established and identifies that local post-LGM ice did not recede and thin as one coherent ice mass. Instead, it separated into multiple topographically-controlled ice masses of different size (alpine icefield, plateau icefield, valley glaciers, and cirque glaciers) in coeval existence. Topography exerted a control on the pattern of local glacier recession and associated moraine distribution. A combination of topographic pinning points (i.e. topographic steps, lateral constriction, and tributary valley incursion), favourable slope gradients (0-15°), and changes in slope appear to have had an important influence on where moraines formed, implying an element of glacier stability at such locations. This provides further insight into non-climatic controls on moraine formation and presence/absence.
This thesis delivers a more detailed understanding of post-LGM glaciation in the Wicklow Mountains. It provides clarification on the scale of YD glaciation and the impact of local topoclimatic processes on cirque glacier initiation and survival. It also provides insight into the significant role of topography in controlling retreat patterns and stability of ice masses, in response to climate amelioration throughout the wider LGIT.
Original languageEnglish
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Award dateJun 2020

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